Principles of Inheritance and Variation

Topic: Gene Mapping and Recombination; Subtopic: Frequency of Recombination

Keyword Definitions:

• Recombination frequency: The percentage of offspring that show new combinations of traits different from the parents due to crossing over.

• Linked genes: Genes located on the same chromosome that tend to be inherited together.

• Crossing over: Exchange of chromosome segments between homologous chromosomes during meiosis, leading to genetic variation.

• Gene mapping: Process of determining the relative positions of genes on a chromosome based on recombination frequencies.

• High frequency recombination: Indicates genes are far apart on a chromosome, allowing more crossing over.

• Low frequency recombination: Indicates genes are close together on a chromosome, reducing the probability of crossing over.

• Centimorgan (cM): Unit of genetic distance representing 1% recombination frequency.

• Independent assortment: Principle that genes on different chromosomes segregate independently during gamete formation.

Lead Question - 2022 (Abroad)
A low frequency recombination indicates that the genes are:
1. Located far apart from each other
2. Located close to each other
3. Not linked
4. Present on different chromosomes
Explanation: The correct answer is Located close to each other. Recombination frequency is inversely related to the physical distance between genes on a chromosome. Genes situated close together are less likely to undergo crossing over during meiosis, resulting in a low recombination frequency. Conversely, genes far apart have higher chances of recombination, producing new allele combinations. Measuring recombination frequency helps in constructing genetic maps, estimating distances between genes, and studying gene linkage. A low recombination percentage indicates strong linkage, which is crucial in predicting inheritance patterns, analyzing genetic disorders, and understanding chromosomal architecture in organisms.

1. Single Correct Answer Type:
Which type of genes usually show high frequency recombination?
1. Closely linked genes
2. Genes far apart on the same chromosome
3. Genes on different chromosomes
4. Mitochondrial genes
Explanation: The correct answer is Genes far apart on the same chromosome. Genes separated by large distances on a chromosome have a higher probability of crossing over during meiosis, leading to new allele combinations in offspring. This high recombination frequency helps determine genetic distance in mapping studies. Closely linked genes exhibit low recombination due to reduced crossover likelihood. Genes on different chromosomes assort independently according to Mendel’s law, which is unrelated to physical distance on a single chromosome. Understanding recombination frequencies is fundamental for predicting inheritance patterns, studying linkage, and constructing chromosomal maps in genetics research.

2. Single Correct Answer Type:
Two genes show 50% recombination frequency. This indicates that they are:
1. Closely linked
2. Far apart on the same chromosome
3. On different chromosomes or unlinked
4. Mitochondrial
Explanation: The correct answer is On different chromosomes or unlinked. A recombination frequency of 50% represents the maximum possible recombination, which occurs either when genes are on separate chromosomes or so far apart on the same chromosome that they assort independently. This follows Mendelian principles of independent assortment. Recombination frequency below 50% indicates linkage. Geneticists use this principle to determine gene positions, map distances, and study hereditary patterns. Accurately interpreting recombination frequency allows prediction of genotypes in crosses, analysis of linkage, and helps in constructing genetic linkage maps that are essential tools for research, breeding, and understanding genome structure.

3. Single Correct Answer Type:
Recombination frequency is usually expressed in:
1. Percentage
2. Centimorgans
3. Both percentage and centimorgans
4. Base pairs
Explanation: The correct answer is Both percentage and centimorgans. Recombination frequency is expressed as a percentage of recombinant offspring or converted into centimorgans (cM), where 1% recombination equals 1 cM. This measure estimates physical distance between genes and helps in constructing genetic maps. Low recombination corresponds to closely linked genes, whereas high recombination suggests genes are far apart or unlinked. Accurate measurement is essential for predicting inheritance patterns, studying genetic disorders, and performing breeding experiments. Centimorgan-based mapping provides a standardized way to relate genetic distances with recombination frequencies in different species and chromosomes.

4. Single Correct Answer Type:
Genes showing low recombination frequency are described as:
1. Linked genes
2. Unlinked genes
3. Mitochondrial genes
4. Sex-linked genes
Explanation: The correct answer is Linked genes. Linked genes reside close together on the same chromosome and tend to be inherited together, exhibiting low recombination frequency due to the reduced likelihood of crossover between them. Their proximity prevents frequent exchange of genetic material, producing offspring with parental combinations of traits. Recombination analysis identifies such linkage and allows construction of genetic maps. Unlinked genes segregate independently, while mitochondrial and sex-linked genes follow distinct inheritance patterns. Understanding linkage and recombination frequencies is essential in genetics for predicting inheritance, breeding strategies, and identifying chromosomal arrangements across species.

5. Single Correct Answer Type:
Which of the following can be inferred from recombination frequency data?
1. Chromosomal distances between genes
2. DNA sequence of genes
3. Protein structure
4. Ribosome activity
Explanation: The correct answer is Chromosomal distances between genes. Recombination frequency indicates the likelihood of crossing over between two genes during meiosis. Low frequency suggests close proximity; high frequency indicates greater distance. This data is essential for constructing genetic linkage maps and determining relative positions of genes. Recombination frequency cannot directly reveal DNA sequence, protein structure, or ribosomal activity. Geneticists use such mapping to study inheritance patterns, predict trait linkage, and perform selective breeding. Measuring recombination provides insight into chromosomal architecture, the physical arrangement of genes, and the probability of co-inheritance of traits in offspring.

6. Single Correct Answer Type:
Which factor primarily affects recombination frequency between two genes?
1. Distance between genes
2. DNA polymerase activity
3. Environmental temperature
4. Ribosomal function
Explanation: The correct answer is Distance between genes. Genes located close together on the same chromosome exhibit low recombination due to limited opportunity for crossover, while genes far apart recombine more frequently. Recombination frequency is directly proportional to intergenic distance. DNA polymerase, temperature, and ribosomal function do not significantly influence meiotic crossing over. Analyzing recombination frequency helps in constructing genetic maps, studying inheritance patterns, and predicting trait linkage. This knowledge is fundamental in genetics, plant and animal breeding, and understanding chromosomal behavior during meiosis, as it provides quantitative information on gene linkage and spatial arrangement on chromosomes.

7. Assertion-Reason Type:
Assertion (A): Low recombination frequency suggests strong linkage between genes.
Reason (R): Genes located close together on a chromosome rarely undergo crossing over.
1. Both A and R are correct, and R explains A
2. Both A and R are correct, but R does not explain A
3. A is correct, R is incorrect
4. A is incorrect, R is correct
Explanation: The correct answer is Both A and R are correct, and R explains A. Low recombination frequency occurs when genes are physically close on a chromosome, reducing the probability of crossover. This strong linkage causes genes to be inherited together in offspring. Crossing over is less frequent over short distances, producing few recombinant gametes. High recombination occurs when genes are far apart or on different chromosomes. Linkage analysis and recombination frequencies help in constructing genetic maps, studying inheritance patterns, and identifying gene positions. Thus, proximity directly explains low recom

Subtopic: Chromosomal Basis of Inheritance

Keyword Definitions:

• Drosophila: A genus of small flies, commonly used as a model organism in genetics studies.

• Autosomes: Chromosomes that are not directly involved in determining sex of an organism.

• Sex Chromosomes: Chromosomes involved in determining the sex of an organism, typically X and Y in Drosophila.

• X-Chromosome: One of the two sex chromosomes, carrying several genes affecting body and eye color in Drosophila.

• Y-Chromosome: Male sex chromosome, generally carries genes for male fertility, not body or eye color.

• Body Color Gene: Gene determining pigmentation of the fly’s body, located on X-chromosome.

• Eye Color Gene: Gene determining eye pigmentation, located on X-chromosome in Drosophila.

Lead Question - 2022 (Abroad)
In Drosophila, the genes for color of body and color of eyes are situated on _______.
1. both the sex chromosomes
2. autosomes
3. Y-chromosome
4. X-chromosome
Explanation: The correct answer is X-chromosome. In Drosophila melanogaster, genes responsible for body color and eye color are sex-linked and specifically located on the X-chromosome. This discovery was fundamental in establishing the chromosomal theory of inheritance. The Y-chromosome carries very few genes related to these traits, and autosomes do not carry these sex-linked characteristics. The inheritance patterns observed in crosses, including reciprocal crosses, confirmed that these traits are X-linked, leading to distinct phenotypic ratios in male and female offspring. This has been extensively used in genetics experiments and teaching.

1. Single Correct Answer Type:
Which chromosome carries eye color genes in Drosophila?
1. Autosomes
2. X-chromosome
3. Y-chromosome
4. Mitochondrial DNA
Explanation: The correct answer is X-chromosome. Eye color genes in Drosophila are located on the X-chromosome, making them sex-linked. Males have only one X-chromosome, so a single allele determines the eye color, while females have two X-chromosomes allowing heterozygosity. Autosomes and Y-chromosome do not carry these eye color genes, making inheritance patterns predictable and fundamental in genetic studies of sex-linked traits.

2. Single Correct Answer Type:
The gene for body color in Drosophila is:
1. Y-linked
2. Autosomal
3. X-linked
4. Mitochondrial
Explanation: The correct answer is X-linked. Body color in Drosophila is controlled by a gene on the X-chromosome. This was demonstrated by Thomas Hunt Morgan. Males being hemizygous show the recessive body color trait when present, whereas females can be carriers. Autosomes, Y-chromosome, and mitochondria do not influence body color in this species, highlighting the significance of X-linked inheritance in phenotypic variation and experimental genetics.

3. Single Correct Answer Type:
Which chromosome does not carry genes for body or eye color in Drosophila?
1. X-chromosome
2. Y-chromosome
3. Both X and Y
4. Autosomes
Explanation: The correct answer is Y-chromosome. The Y-chromosome in Drosophila primarily carries genes for male fertility and does not include genes for body or eye color. These traits are X-linked, as demonstrated in classical crosses. The Y-chromosome’s lack of pigmentation genes explains why males show recessive traits when only one X-chromosome is present. Autosomes and X-chromosome carry other traits, but Y is not involved in sex-linked body and eye color inheritance.

4. Single Correct Answer Type:
Sex-linked inheritance in Drosophila was established by observing which traits?
1. Wing length
2. Eye and body color
3. Bristle pattern
4. Fertility
Explanation: The correct answer is Eye and body color. Thomas Hunt Morgan’s experiments with Drosophila showed that eye color (red vs. white) and body color (gray vs. ebony) are X-linked. Reciprocal crosses revealed distinct phenotypic ratios in males and females. These traits were critical in confirming the chromosomal theory of inheritance, demonstrating sex linkage, and differentiating sex-linked from autosomal inheritance patterns, forming a basis for modern genetics and understanding X-linked trait expression.

5. Single Correct Answer Type:
Reciprocal crosses in Drosophila show:
1. Autosomal inheritance
2. Maternal inheritance
3. X-linked inheritance
4. Y-linked inheritance
Explanation: The correct answer is X-linked inheritance. Reciprocal crosses using eye color and body color traits demonstrated that the phenotype in male offspring depends on the X-chromosome contributed by the mother. Males have only one X-chromosome and express the trait, whereas females may be carriers. This pattern does not occur for autosomal or Y-linked genes, confirming X-linked inheritance as the mechanism controlling these traits in Drosophila.

6. Single Correct Answer Type:
Which type of inheritance explains white-eyed male Drosophila when crossed with red-eyed females?
1. Autosomal recessive
2. X-linked recessive
3. Y-linked dominant
4. Mitochondrial
Explanation: The correct answer is X-linked recessive. The white-eye allele is recessive and located on the X-chromosome. Males inherit only one X from the mother; if it carries the white-eye allele, they show the phenotype. Females require two copies for expression. This inheritance pattern demonstrates X-linkage and recessivity, crucial for understanding sex-linked trait expression, genetic mapping, and predicting progeny ratios in experimental genetics.

7. Assertion-Reason Type:
Assertion (A): Body color and eye color in Drosophila are X-linked.
Reason (R): Males inherit only one X-chromosome from the mother and express recessive traits.
1. Both A and R are correct, and R is the correct explanation of A
2. Both A and R are correct, but R is not the correct explanation of A
3. A is correct, R is false
4. A is false, R is true
Explanation: The correct answer is Both A and R are correct, and R is the correct explanation of A. The X-linked inheritance of body and eye color causes males to show recessive traits if their single X-chromosome carries the allele. Females with two X-chromosomes may be carriers. This explains the observed phenotypic ratios in reciprocal crosses and demonstrates X-linked inheritance, forming a cornerstone of Drosophila genetics experiments.

8. Matching Type:
Match the trait with chromosome location in Drosophila:
A. Eye color → (i) Y-chromosome
B. Body color → (ii) Autosomes
C. Fertility genes → (iii) X-chromosome
D. Male-determining factor → (iv) Y-chromosome
1. A-(iii), B-(iii), C-(iv), D-(iv)
2. A-(iv), B-(ii), C-(iii), D-(i)
3. A-(iii), B-(ii), C-(i), D-(iv)
4. A-(ii), B-(iii), C-(iv), D-(i)
Explanation: Correct matching is A-(iii), B-(iii), C-(iv), D-(iv). Eye and body color genes are on X-chromosome; male fertility genes and male-determining factor are on Y-chromosome. This differentiation explains sex-linked

Topic: Polygenic Inheritance; Subtopic: Quantitative Traits

Keyword Definitions:

• Polygenic Inheritance: Traits controlled by two or more genes showing continuous variation, like skin, hair, or eye color.

• Quantitative Traits: Traits that exhibit a range of phenotypes rather than discrete categories.

• Genotype: Genetic constitution of an organism, e.g., AABBCC.

• Phenotype: Observable trait or physical expression of a genotype.

• F1 Generation: The first filial generation obtained from a cross of two parental organisms.

Lead Question - 2022 (Abroad)
Assuming that fur colour of an animal is dark, range of colour shade and white. A cross is made between a male (AABBCC) with dark fur colour and a female (aabbcc) with white fur colour. What would be the fur colour of F1 generation?
1. All intermediate colour
2. Range of colour shade
3. All dark colour
4. All white colour
Explanation: In this polygenic inheritance, the male is homozygous dominant (AABBCC) and female is homozygous recessive (aabbcc). Each F1 offspring receives one allele from each parent per gene, producing AaBbCc genotype. This results in an intermediate fur colour, as additive effects of multiple genes blend to create a phenotype between the extremes of dark and white, showing the characteristic continuous variation of polygenic traits.

1. Single Correct Answer Type:
In polygenic inheritance, which statement is correct?
1. Traits are controlled by a single gene
2. Traits show continuous variation
3. Traits are unaffected by environment
4. Traits are always dominant or recessive
Explanation: Polygenic inheritance involves multiple genes, and each contributes a small effect to the phenotype, resulting in continuous variation such as height, skin color, and fur color. Environmental factors may also influence these traits. Unlike Mendelian traits, polygenic traits do not fall into discrete categories but show a gradient of expression across a population.

2. Single Correct Answer Type:
What genotype would an intermediate F1 offspring show in a cross AABBCC × aabbcc?
1. AaBbCc
2. AABbCc
3. aaBBCC
4. AABBCC
Explanation: Each F1 offspring receives one allele from each parent per gene. Crossing homozygous dominant (AABBCC) with homozygous recessive (aabbcc) results in all offspring having AaBbCc genotype. This heterozygous combination for all three genes produces intermediate phenotype because additive gene effects blend the contributions of dominant and recessive alleles, typical of polygenic inheritance.

3. Single Correct Answer Type:
Which term best describes the range of phenotypes in polygenic traits?
1. Discontinuous variation
2. Continuous variation
3. Monogenic effect
4. Codominance
Explanation: Polygenic traits exhibit continuous variation because multiple genes contribute cumulatively to the phenotype. Instead of discrete categories, phenotypes show a smooth gradient from one extreme to another. Examples include height, skin color, and fur color in animals. Environmental factors may further influence the distribution and intensity of traits.

4. Single Correct Answer Type:
If AaBbCc individuals are crossed among themselves, what ratio of phenotypes is expected?
1. All intermediate
2. Range of shades
3. All dark
4. All white
Explanation: Crossing F1 heterozygotes (AaBbCc) produces offspring with different combinations of alleles, leading to a range of shades of fur color. This demonstrates additive effects, where each dominant allele contributes to pigmentation intensity. The resulting distribution forms a bell-shaped curve typical of polygenic inheritance, with extreme phenotypes less frequent than intermediates.

5. Single Correct Answer Type:
In polygenic inheritance, the environmental effect is:
1. Negligible
2. Sometimes influential
3. Deterministic
4. Dominant over genes
Explanation: Environmental factors are sometimes influential in polygenic traits. For instance, nutrition can affect height, temperature may alter fur color, and sunlight exposure can influence skin pigmentation. These traits do not follow strict Mendelian ratios, as phenotype is the combined effect of multiple genes and environmental inputs, producing continuous variation.

6. Single Correct Answer Type:
Which of the following is an example of polygenic inheritance?
1. ABO blood group
2. Human height
3. Flower color in Mendel’s pea
4. Wrinkled vs smooth peas
Explanation: Human height is a classic polygenic trait, controlled by multiple genes, each contributing additively to the phenotype. Like fur color in animals, it shows continuous variation with no discrete categories. Environmental factors such as nutrition further influence its expression, demonstrating the cumulative and multifactorial nature of polygenic inheritance.

7. Assertion-Reason Type:
Assertion (A): F1 offspring from AABBCC × aabbcc show uniform fur color.
Reason (R): F1 are heterozygous for all genes, producing intermediate phenotype.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true
Explanation: Both Assertion and Reason are true, and the Reason explains the Assertion. The heterozygous genotype AaBbCc in F1 individuals leads to uniform intermediate fur color because each dominant allele contributes additively to pigmentation. This demonstrates the principle of polygenic inheritance where multiple genes blend to produce intermediate phenotypes.

8. Matching Type:
Match the gene with its effect:
A. Dominant allele → (i) Contributes to dark fur
B. Recessive allele → (ii) Contributes to light fur
C. Homozygous dominant → (iii) Maximum pigmentation
D. Heterozygous → (iv) Intermediate pigmentation
1. A-(i), B-(ii), C-(iii), D-(iv)
2. A-(ii), B-(i), C-(iv), D-(iii)
3. A-(i), B-(ii), C-(iv), D-(iii)
4. A-(ii), B-(i), C-(iii), D-(iv)
Explanation: Correct matching is A-(i), B-(ii), C-(iii), D-(iv). Dominant alleles add to dark coloration, recessive alleles reduce pigment. Homozygous dominant results in maximum pigmentation, while heterozygotes show intermediate phenotypes. This is typical for polygenic inheritance, where cumulative effects of multiple genes determine the phenotype.

9. Fill in the Blanks Type:
Polygenic traits exhibit _______ variation in the population.
1. Discontinuous
2. Continuous
3. Dichotomous
4. Monogenic
Explanation: The correct answer is continuous variation. Polygenic traits are influenced by multiple genes whose additive effects produce a gradient of phenotypes rather than discrete categories. Environmental factors can further modulate these traits. Examples include height, fur color, and skin pigmentation, all showing a smooth distribution across populations.

Subtopic: Chromosomal and Genetic Disorders

• Haemophilia: A sex-linked recessive disorder causing defective blood coagulation.

• Down's Syndrome: Genetic disorder caused by the presence of an extra chromosome 21.

• Phenylketonuria (PKU): An inborn error of metabolism lacking enzyme converting phenylalanine to tyrosine.

• Klinefelter's Syndrome: Genetic condition in males with an extra X chromosome (44+XXY).

• Chromosome: Thread-like structure carrying genetic information in the form of genes.

• Sex-linked inheritance: Traits determined by genes located on sex chromosomes.

• Genetic disorder: Condition caused by abnormalities in an individual's DNA.

• Inborn error of metabolism: Genetic defect affecting metabolism due to missing or defective enzymes.

• Autosomal disorder: Genetic disorder caused by mutations in non-sex chromosomes.

• Recessive trait: A trait expressed only when two copies of the gene are present.

• Karyotype: Chromosome complement of an individual, showing number and structure.

Lead Question - 2022 (Abroad)

Match List-I with List-II:

List-I

(a) Haemophilia
(b) Down's Syndrome
(c) Phenylketonuria
(d) Klinefelter's Syndrome

List-II

(i) Inborn error of metabolism which lacks an enzyme that converts phenylalanine into tyrosine
(ii) Sex-linked recessive disorder defect in blood coagulation
(iii) Presence of additional copy of X-chromosome (44+XXY)
(iv) Additional copy of chromosome number 21

1. (ii), (iv), (i), (iii)

2. (iv), (ii), (i), (iii)

3. (ii), (iii), (i), (iv)

4. (i), (ii), (iii), (iv)

Explanation: Correct matching: Haemophilia (a) is a sex-linked recessive disorder affecting blood clotting (ii); Down's Syndrome (b) results from an extra chromosome 21 (iv); Phenylketonuria (c) is an inborn metabolic disorder lacking enzyme converting phenylalanine to tyrosine (i); Klinefelter's (d) shows additional X chromosome (iii). Answer: 1

Q1: Phenylketonuria is caused due to deficiency of which enzyme?

1. Tyrosinase

2. Phenylalanine hydroxylase

3. Glucose-6-phosphate dehydrogenase

4. Amylase

Explanation: Phenylketonuria (PKU) results from the lack of phenylalanine hydroxylase, preventing conversion of phenylalanine to tyrosine. Tyrosinase affects melanin, G6PD deficiency causes hemolysis, amylase digests starch. Early diagnosis prevents mental retardation. Answer: Phenylalanine hydroxylase. Answer: 2

Q2: Klinefelter's syndrome typically affects:

1. Females with XXY

2. Males with XXY

3. Males with XYY

4. Females with XXX

Explanation: Klinefelter's syndrome occurs in males with an extra X chromosome (44+XXY). It results in hypogonadism, infertility, and taller stature. XYY males have Jacob’s syndrome, XXX females may have triple X. Answer: Males with XXY. Answer: 2

Q3: Down's Syndrome is caused by:

1. Trisomy 21

2. Monosomy X

3. Duplication of X chromosome

4. Mutation in hemoglobin gene

Explanation: Down's Syndrome results from trisomy of chromosome 21, leading to characteristic physical features and intellectual disability. Monosomy X is Turner’s syndrome, X duplication is Klinefelter’s, hemoglobin mutation causes sickle cell. Answer: Trisomy 21. Answer: 1

Q4: Haemophilia is inherited in which pattern?

1. Autosomal dominant

2. Autosomal recessive

3. X-linked recessive

4. Y-linked

Explanation: Haemophilia is an X-linked recessive disorder. Males are affected if they inherit the defective gene from carrier mothers, while females are usually carriers. Autosomal inheritance affects both sexes equally. Y-linked disorders affect only males. Answer: X-linked recessive. Answer: 3

Q5: Which of the following is an inborn error of metabolism?

1. Down's Syndrome

2. Klinefelter's Syndrome

3. Phenylketonuria

4. Haemophilia

Explanation: Phenylketonuria is an inborn metabolic disorder caused by enzyme deficiency affecting amino acid metabolism. Down’s and Klinefelter are chromosomal disorders, Haemophilia is sex-linked. Early detection and dietary management are important. Answer: Phenylketonuria. Answer: 3

Q6: Which disorder results in additional X chromosome in males?

1. Down's Syndrome

2. Klinefelter's Syndrome

3. Turner Syndrome

4. Haemophilia

Explanation: Klinefelter's syndrome in males results from an extra X chromosome (44+XXY), causing hypogonadism and infertility. Turner’s syndrome is female monosomy X, Down’s is trisomy 21, Haemophilia is X-linked recessive. Answer: Klinefelter's Syndrome. Answer: 2

Q7: Assertion (A): Haemophilia primarily affects males.
Reason (R): Haemophilia is an X-linked recessive disorder.

1. (A) is correct but R is not correct

2. (A) is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: Haemophilia is X-linked recessive; males with one X chromosome express the disorder if the defective gene is present. Females are usually carriers with two X chromosomes. Both assertion and reason are correct, and reason explains assertion. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the disorder with its chromosome abnormality/type:

A. Haemophilia    1. Sex-linked recessive
B. Down's Syndrome    2. Trisomy 21
C. Phenylketonuria    3. Inborn metabolic defect
D. Klinefelter's Syndrome    4. XXY male

1. A-1, B-2, C-3, D-4

2. A-2, B-1, C-4, D-3

3. A-1, B-3, C-2, D-4

4. A-3, B-2, C-1, D-4

Explanation: Correct matching: Haemophilia is X-linked recessive, Down's is trisomy 21, Phenylketonuria is inborn metabolic defect, Klinefelter's is XXY male. This helps in differentiating chromosomal and metabolic disorders. Answer: A-1, B-2, C-3, D-4. Answer: 1

Q9: Down's Syndrome is caused by ______.

1. Trisomy 21

2. Monosomy X

3. XXY karyotype

4. Enzyme deficiency

Explanation: Down's Syndrome is caused by trisomy of chromosome 21, resulting in intellectual disability and characteristic facial features. Monosomy X causes Turner syndrome, XXY causes Klinefelter’s, enzyme deficiency causes PKU. Answer: Trisomy 21. Answer: 1

Q10: Which statements about genetic disorders are correct?

1. Haemophilia is X-linked recessive

2. PKU is an inborn error of metabolism

3. Klinefelter's is caused by extra Y chromosome

4. Down's Syndrome is trisomy 21

Explanation: Correct statements: Haemophilia is X-linked recessive, PKU is a metabolic disorder, Down’s is trisomy 21. Klinefelter’s involves extra X, not Y chromosome. Answer: 1, 2, 4

Topic: Sex-linked Inheritance

Subtopic: Haemophilia

• Haemophilia: A genetic disorder causing defective blood clotting, usually X-linked recessive.

• X-linked recessive traits: Traits determined by genes on X chromosome, predominantly expressed in males.

• Gene inheritance: Transmission of genetic material from parents to offspring as per Mendelian rules.

• Sex-linked traits: Traits associated with genes on sex chromosomes (X or Y).

• Allele: Alternative form of a gene at the same locus on homologous chromosomes.

• Chromosome: DNA molecule carrying genetic information in the form of genes.

• Autosome: Any chromosome other than X or Y.

• Carrier: Individual carrying a recessive gene but not showing the trait phenotypically.

• Dominant: Allele expressed in heterozygous condition.

• Recessive: Allele expressed only in homozygous condition.

• Pedigree analysis: Study of inheritance pattern of traits across generations in a family.

Lead Question - 2022 (Abroad)

Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R)
Assertion(A): A father will never pass the gene for haemophilia to his sons
Reason (R) : Haemophilia is sex-linked (X-linked recessive traits).
In the light of the above statements, choose the correct answer from the options given below

1. (A) is correct but R is not correct

2. (A) is not correct but (R) is correct

3. Both (A) and (R) are correct (R) is the correct explanation of (A)

4. Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Explanation: The father passes Y chromosome to sons and X to daughters. Haemophilia being X-linked recessive cannot be inherited by sons from the father. Daughters may become carriers if the mother provides normal or affected X. Thus, both assertion and reason are correct, and R correctly explains A. Answer: 3

Q1: Which of the following is a characteristic feature of X-linked recessive inheritance?

1. Trait appears equally in both sexes

2. Trait is transmitted from father to son

3. Trait appears more frequently in males

4. Trait skips only one generation

Explanation: X-linked recessive traits appear predominantly in males because they have a single X chromosome. Females with one affected X are carriers and usually asymptomatic. Transmission occurs through carrier mothers to sons. This pattern explains male predominance in X-linked recessive disorders. Answer: Trait appears more frequently in males. Answer: 3

Q2: A mother is a carrier of haemophilia and the father is normal. What is the probability of their son having haemophilia?

1. 0%

2. 25%

3. 50%

4. 100%

Explanation: A carrier mother has genotype XHXh. Sons inherit X from mother and Y from father. Probability of son receiving affected Xh is 50%, leading to haemophilia. Father does not contribute X to sons, so cannot influence risk. Therefore, each son has a 50% chance. Answer: 50%. Answer: 3

Q3: In a pedigree chart, how is a female carrier of haemophilia represented?

1. Shaded circle

2. Unshaded circle

3. Half-shaded circle

4. Shaded square

Explanation: In pedigrees, circles indicate females. Half-shaded circle denotes carrier of X-linked recessive trait like haemophilia. Fully shaded indicates affected, unshaded indicates normal. This symbol helps track inheritance in families and identify carriers who may transmit trait to offspring. Answer: Half-shaded circle. Answer: 3

Q4: Which chromosome determines male sex in humans?

1. X chromosome

2. Y chromosome

3. Both X and Y equally

4. Autosome 21

Explanation: The Y chromosome carries SRY gene, initiating male development. Males inherit X from mother and Y from father. Presence of Y determines male sex, absence leads to female. Fathers pass Y to sons and X to daughters. This is essential in understanding inheritance of sex-linked traits. Answer: Y chromosome. Answer: 2

Q5: Which of the following is true for daughters of a haemophilic father and normal mother?

1. All daughters affected

2. All daughters carriers

3. All daughters normal

4. Half daughters affected

Explanation: A haemophilic father passes Xh to daughters and Y to sons. If the mother is normal (XH), daughters inherit XH from mother and Xh from father, making them carriers. They do not show disease but can transmit the affected gene to future generations. Answer: All daughters carriers. Answer: 2

Q6: Which mutation leads to haemophilia A?

1. Mutation in F8 gene

2. Mutation in F9 gene

3. Mutation in F7 gene

4. Mutation in HBB gene

Explanation: Haemophilia A is caused by mutation in F8 gene coding for coagulation factor VIII. This X-linked recessive mutation prevents proper blood clotting. Identification of mutations helps carrier detection and genetic counselling. F9 mutations cause haemophilia B, and HBB mutation causes beta-thalassemia. Answer: Mutation in F8 gene. Answer: 1

Q7: Assertion (A): Female carriers of X-linked disorders rarely show symptoms.
Reason (R): One X chromosome is inactivated randomly in females.

1. (A) is correct but R is not correct

2. (A) is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: Random X-inactivation (lyonization) in females ensures one X is active, reducing manifestation of X-linked recessive disorders. Female carriers typically remain asymptomatic or mildly affected. Both assertion and reason are correct, and reason explains assertion. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the disorders with their genes:

A. Haemophilia A    1. F9 gene
B. Haemophilia B    2. F8 gene
C. Duchenne Muscular Dystrophy    3. DMD gene
D. Colour blindness    4. OPN1LW/OPN1MW genes

1. A-2, B-1, C-3, D-4

2. A-1, B-2, C-3, D-4

3. A-2, B-1, C-4, D-3

4. A-1, B-2, C-4, D-3

Explanation: Haemophilia A arises from F8, Haemophilia B from F9, Duchenne Muscular Dystrophy from DMD, and red-green colour blindness from OPN1LW/OPN1MW genes. Matching correctly identifies genes responsible for X-linked disorders, assisting genetic diagnosis and counselling. Answer: A-2, B-1, C-3, D-4. Answer: 1

Q9: In X-linked recessive disorders, a female with one affected X chromosome is called a ______.

1. Normal

2. Carrier

3. Homozygous

4. Affected

Explanation: A female with one normal and one affected X chromosome is a carrier of X-linked recessive disorders. Carriers usually show no symptoms but can transmit the defective gene to offspring. Understanding carrier status is essential in genetic counselling for families at risk of haemophilia. Answer: Carrier. Answer: 2

Q10: Which of the following statements are correct?

1. Fathers pass X-linked traits only to daughters

2. Mothers can transmit X-linked traits to sons

3. Haemophilia is manifested in males only

4. X-linked recessive traits are more common in females

Explanation: Fathers transmit X-linked traits exclusively to daughters; sons receive Y chromosome. Mothers transmit X-linked traits to sons. Haemophilia primarily affects males, females are carriers. X-linked recessive traits are rare in females. Therefore, correct statements are 1 and 2. Answer: 1, 2

Topic: Sex-linked Inheritance
Subtopic: X-linked Recessive Traits

Keyword Definitions:
- Colour blindness: X-linked recessive condition affecting vision of red and green colors.
- Progeny: Offspring of a genetic cross.
- X-linked gene: Gene located on the X chromosome.
- Recessive trait: Trait expressed only when two recessive alleles are present.
- Carrier female: Female with one normal and one affected X chromosome.
- Homozygous: Having two identical alleles for a gene.
- Heterozygous: Having two different alleles for a gene.
- Genotype: Genetic constitution of an organism.
- Phenotype: Observable trait of an organism.
- Mendelian inheritance: Pattern of inheritance for dominant and recessive traits.
- Sex-linked inheritance: Inheritance pattern associated with genes on sex chromosomes.

Lead Question - 2022:
If a colour blind female marries a man whose mother was also colour blind, what are the chances of her progeny having colour blindness?
(1) 50%
(2) 75%
(3) 100%
(4) 25%

Explanation: The correct answer is (3) 100%. Colour blindness is an X-linked recessive trait. A female affected (XcXc) marries a male whose mother was colour blind (XcY). All sons receive Xc from mother, daughters receive Xc from both parents, resulting in all progeny being colour blind.

1. Single Correct Answer:
Colour blindness is inherited through which type of chromosome?
(a) Y chromosome
(b) X chromosome
(c) Autosomes
(d) Mitochondrial DNA
Explanation: Colour blindness is an X-linked recessive trait. It is associated with genes on the X chromosome. Males (XY) express the trait if X carries the recessive allele. Autosomes and Y chromosome do not carry this gene, and mitochondrial DNA inheritance is maternal only.

2. Single Correct Answer:
A carrier female for colour blindness has which genotype?
(a) XcXc
(b) XX
(c) XcX
(d) XY
Explanation: A carrier female has genotype XcX. She carries one normal X allele and one allele for colour blindness. This heterozygous state allows her to transmit the trait to offspring without expressing it herself, as recessive traits require two affected alleles to show phenotype.

3. Single Correct Answer:
What is the phenotype of a male with genotype XcY?
(a) Normal vision
(b) Colour blind
(c) Carrier
(d) Mosaic
Explanation: Males with genotype XcY are colour blind because they have only one X chromosome carrying the recessive allele. Males cannot be carriers as they lack a second X to mask the recessive gene, so the trait is fully expressed in the phenotype.

4. Single Correct Answer:
If a carrier female marries a normal male, what percentage of sons will be colour blind?
(a) 25%
(b) 50%
(c) 75%
(d) 100%
Explanation: 50% of sons will be colour blind. Sons inherit Y from father and X from mother. Carrier female has XcX, so half the sons receive Xc, resulting in colour blindness. The other half receive normal X, showing normal vision.

5. Single Correct Answer:
Which of the following is true for daughters of a colour blind male and normal female?
(a) All daughters are colour blind
(b) All daughters are carriers
(c) Half daughters are colour blind
(d) No daughters carry the trait
Explanation: All daughters will be carriers. Male XcY passes Xc to daughters, female provides normal X. Daughters (XcX) carry the allele without expressing the trait due to heterozygosity, showing normal vision but able to transmit the trait to next generation.

6. Single Correct Answer:
Which is a typical example of X-linked recessive inheritance?
(a) Colour blindness
(b) Sickle cell anemia
(c) Down syndrome
(d) Cystic fibrosis
Explanation: Colour blindness is a classic X-linked recessive trait. It affects males predominantly and is transmitted via X chromosome. Sickle cell anemia and cystic fibrosis are autosomal recessive, and Down syndrome is chromosomal trisomy. Hence, colour blindness illustrates sex-linked inheritance patterns.

7. Assertion-Reason MCQ:
Assertion (A): Colour blindness affects more males than females.
Reason (R): It is an X-linked recessive trait.
(a) Both A and R are true, R is correct explanation of A
(b) Both A and R are true, R is not correct explanation of A
(c) A is true, R is false
(d) A is false, R is true
Explanation: Option (a) is correct. Males are more frequently affected due to having a single X chromosome. A recessive allele on the X manifests the trait in males. Females require two recessive alleles, making the frequency much lower. Both assertion and reason are true, and R explains A.

8. Matching Type MCQ:
Match individuals with their genotype:
List - I List - II
(a) Colour blind female (i) XcXc
(b) Carrier female (ii) XcX
(c) Colour blind male (iii) XcY
(d) Normal male (iv) XY
Options:
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-iii, b-iv, c-i, d-ii
(4) a-iv, b-iii, c-ii, d-i
Explanation: Option (1) is correct. Colour blind female XcXc, carrier XcX, male XcY is affected, normal male XY unaffected. This classification ensures accurate understanding of X-linked inheritance patterns in progeny analysis and predicting offspring phenotypes.

9. Fill in the Blanks:
A male with XcY genotype will have _______ vision.
(a) Normal
(b) Colour blind
(c) Carrier
(d) Mosaic
Explanation: A male with genotype XcY will be colour blind. Males have only one X chromosome, so a recessive allele expresses the trait. There is no second X to mask the recessive allele, unlike females, ensuring complete manifestation of X-linked recessive conditions.

10. Choose the Correct Statements:
Identify the correct statements:
1. Colour blindness is X-linked recessive.
2. Carrier females can transmit the trait.
3. All daughters of colour blind males are colour blind.
4. Males are more commonly affected than females.
Options:
(a) 1, 2, 3
(b) 1, 2, 4
(c) 2, 3, 4
(d) 1, 3, 4
Explanation: Option (b) is correct. Colour blindness is X-linked recessive. Carrier females transmit the trait to offspring. Males are more affected because they possess only one X chromosome. Statement 3 is incorrect; daughters inherit one X from father and one from mother, becoming carriers rather than affected.

Topic: Gene Mapping
Subtopic: Recombination Frequency and Gene Sequence

Keyword Definitions:
- Recombination frequency: The percentage of offspring in which a crossover occurs between two genes.
- Gene sequence: Linear arrangement of genes on a chromosome.
- Chromosome: DNA molecule carrying genetic material.
- Crossover: Exchange of genetic material between homologous chromosomes.
- Map unit (centimorgan): Unit representing 1% recombination frequency.
- Linked genes: Genes located close together on the same chromosome.
- Genetic mapping: Determining the order of genes based on recombination frequencies.
- Linear chromosome: Chromosome with genes arranged in a line.
- Allele: Different forms of a gene.
- Distance between genes: Measured using recombination frequency.
- Marker gene: A known gene used to determine linkage.

Lead Question - 2022:
The recombination frequency between the genes a & c is 5%, b & c is 15%, b & d is 9%, a & b is 20%, c & d is 24% and a & d is 29%. What will be the sequence of these genes on a linear chromosome?
(1) d, b, a, c
(2) a, b, c, d
(3) a, c, b, d
(4) a, d, b, c

Explanation: The correct sequence is (3) a, c, b, d. Recombination frequencies indicate relative distances: a-c 5%, c-b 10% (from b-c 15% minus a-c 5%), b-d 9%. Summing distances linearly gives a-c-b-d arrangement. This sequence accurately reflects the smallest cumulative distances, showing proper gene mapping on the chromosome.

1. Single Correct Answer:
Which gene pair shows the least recombination frequency?
(a) a & b
(b) a & c
(c) b & d
(d) c & d
Explanation: The lowest recombination frequency is between a & c (5%). A lower frequency indicates genes are closely linked on a chromosome. Other pairs like a-b (20%), b-d (9%), and c-d (24%) are farther apart. Therefore, a & c is the closest pair reflecting minimal crossover events.

2. Single Correct Answer:
Which gene pair has the maximum recombination frequency?
(a) a & c
(b) a & d
(c) b & d
(d) b & c
Explanation: The maximum recombination frequency is a & d (29%). High recombination frequency shows that these genes are farthest apart on the chromosome. Other pairs like a-c 5%, b-d 9%, b-c 15% are closer. Hence, a & d represent the most distant gene pair on this linear chromosome.

3. Single Correct Answer:
What is the distance in map units between genes b & c?
(a) 5 cM
(b) 10 cM
(c) 15 cM
(d) 20 cM
Explanation: Distance in map units equals recombination frequency. b & c have 15% recombination, but considering a-c 5%, distance between c and b is 10 cM. Each percentage corresponds to 1 map unit. This confirms correct gene spacing on the chromosome for genetic mapping and linkage analysis.

4. Single Correct Answer:
If a & b distance is 20 cM, which gene lies between them?
(a) c
(b) d
(c) none
(d) both c & d
Explanation: Gene c lies between a & b. a-c is 5%, b-c is 15%, summing 20% which matches a-b distance. No other gene fits this spacing accurately. This confirms gene c’s intermediate position in the linear sequence a-c-b-d, crucial for mapping chromosome structure.

5. Single Correct Answer:
Which two genes are separated by 9% recombination?
(a) a & c
(b) b & d
(c) c & d
(d) a & b
Explanation: Recombination frequency between b & d is 9%. This indicates moderate linkage; they are neither very close nor far apart. Other pairs, a-c 5%, c-d 24%, a-b 20% show closer or farther distances. Therefore, b & d are separated by 9 cM on the chromosome.

6. Single Correct Answer:
Which gene is at one end of the chromosome sequence?
(a) a
(b) b
(c) c
(d) d
Explanation: In the sequence a-c-b-d, genes a and d are at the ends. Here, gene a is considered at one end. Genes c and b are internal. Recombination frequencies support this positioning, confirming the linear order and terminal location of gene a on the chromosome.

7. Assertion-Reason MCQ:
Assertion (A): Recombination frequency between a & c is smallest.
Reason (R): Closely linked genes show lower recombination frequencies.
(a) Both A and R are true, R is correct explanation of A
(b) Both A and R are true, R is not correct explanation of A
(c) A is true, R is false
(d) A is false, R is true
Explanation: Option (a) is correct. Recombination frequency between a & c is 5%, the smallest among all pairs. Closely linked genes undergo fewer crossovers, reducing recombination frequency. Both the assertion and reason are correct, and the reason directly explains why a & c show minimal recombination.

8. Matching Type MCQ:
Match the gene pairs with recombination frequency:
List - I List - II
(a) a & c (i) 5%
(b) b & d (ii) 9%
(c) b & c (iii) 15%
(d) a & d (iv) 29%
Options:
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-iii, b-iv, c-i, d-ii
(4) a-iv, b-iii, c-ii, d-i
Explanation: Option (1) is correct. a & c = 5%, b & d = 9%, b & c = 15%, a & d = 29%. Matching these frequencies with gene pairs confirms their correct genetic distances and validates the linear chromosome sequence a-c-b-d accurately.

9. Fill in the Blanks:
The gene sequence on the chromosome based on recombination frequencies is _______.
(a) d-b-a-c
(b) a-b-c-d
(c) a-c-b-d
(d) a-d-b-c
Explanation: The correct sequence is a-c-b-d. Recombination frequencies indicate distances: a-c 5%, c-b 10%, b-d 9%. Summing intermediate distances ensures the smallest cumulative recombination. This accurately positions genes in linear order, supporting precise genetic mapping on the chromosome.

10. Choose the Correct Statements:
Identify the correct statements:
1. Recombination frequency indicates gene distance.
2. Genes with low recombination frequency are closely linked.
3. Genes a & d are the closest pair.
4. The linear gene sequence is a-c-b-d.
Options:
(a) 1, 2, 3
(b) 1, 2, 4
(c) 2, 3, 4
(d) 1, 3, 4
Explanation: Option (b) is correct. Recombination frequency reflects gene distances. Closely linked genes, like a & c, have low recombination. The correct linear sequence based on cumulative distances is a-c-b-d. Genes a & d are farthest apart, so statement 3 is incorrect.

Topic: Mendelian Genetics
Subtopic: Gene Linkage and Independent Assortment

Keyword Definitions:
• Mendel’s Law of Independent Assortment: Alleles of different genes segregate independently during gamete formation.
• Gene Linkage: Genes located close together on the same chromosome tend to be inherited together.
• Chromosome: Thread-like structure of DNA and proteins carrying genetic information.
• Allele: Alternative forms of a gene present at the same locus.
• Gamete: Haploid reproductive cell that fuses during fertilization.
• Segregation: Separation of alleles during gamete formation.
• Recombination: Exchange of genetic material between homologous chromosomes.
• Linkage Group: Set of genes on the same chromosome.
• Crossover: Process where homologous chromosomes exchange segments during meiosis.
• Independent Assortment: Random distribution of alleles of unlinked genes into gametes.

Lead Question (2022):
Given below are two statements: one is labelled as
Assertion (A): Mendel’s law of Independent assortment does not hold good for the genes that are located closely on the same chromosome.
Reason (R): Closely located genes assort independently.
In the light of the above statements, choose the correct answer from the options given below:
1. Both (A) and (R) are correct but (R) is not the correct explanation (A)
2. (A) is correct but (R) is not correct
3. (A) is not correct but (R) is correct
4. Both (A) and (R) are correct and (R) is the correct explanation of (A)

Explanation: The correct answer is 2. (A) is correct because Mendel’s law of independent assortment fails for genes located closely on the same chromosome due to linkage. (R) is incorrect because closely linked genes do not assort independently. Crossing over may separate them, but independent assortment is not strictly followed.

Guessed MCQs:

1. Which process can break linkage between closely located genes?
Options:
(a) Crossing over
(b) Independent assortment
(c) Mitosis
(d) Fertilization
Explanation: The correct answer is (a) Crossing over. During meiosis, homologous chromosomes exchange segments, separating linked genes and producing recombinant gametes. Independent assortment applies to unlinked genes, while mitosis and fertilization do not alter linkage patterns.

2. Two genes located on different chromosomes show:
Options:
(a) Independent assortment
(b) Complete linkage
(c) Partial linkage
(d) Epistasis
Explanation: The correct answer is (a) Independent assortment. Genes on different chromosomes segregate independently into gametes. Complete or partial linkage occurs only for genes on the same chromosome, while epistasis refers to interaction between genes affecting phenotypes.

3. Assertion-Reason MCQ:
Assertion (A): Linked genes are inherited together.
Reason (R): They are located far apart on the same chromosome.
Options:
(a) Both A and R are true, R explains A
(b) Both A and R are true, R does not explain A
(c) A is true, R is false
(d) A is false, R is true
Explanation: The correct answer is (c). Linked genes are inherited together because they are close together on the same chromosome. If genes are far apart, crossing over may separate them. Hence, the reason given is false, but the assertion is correct.

4. Matching Type MCQ:
Match the type of gene interaction with its effect on inheritance:
List - I List - II
(a) Linked genes (i) Tend to be inherited together
(b) Unlinked genes (ii) Follow independent assortment
(c) Epistatic genes (iii) One gene masks another
Options:
1. a-i, b-ii, c-iii
2. a-ii, b-i, c-iii
3. a-iii, b-i, c-ii
4. a-i, b-iii, c-ii
Explanation: The correct answer is 1. Linked genes are inherited together, unlinked genes follow Mendel’s independent assortment, and epistatic genes influence or mask the effect of other genes, affecting phenotypic ratios without altering the basic segregation of alleles.

5. Which phenomenon produces new allele combinations in linked genes?
Options:
(a) Recombination
(b) Independent assortment
(c) Mitosis
(d) Cloning
Explanation: The correct answer is (a) Recombination. Crossing over between homologous chromosomes during meiosis produces recombinant gametes with new combinations of linked alleles. Independent assortment applies to unlinked genes, while mitosis and cloning do not generate new allele combinations.

6. Single Correct Answer:
Genes located on the same chromosome are called:
Options:
(a) Linked genes
(b) Unlinked genes
(c) Allelic genes
(d) Mutant genes
Explanation: The correct answer is (a) Linked genes. Genes physically close on the same chromosome are inherited together more often than predicted by independent assortment. Unlinked genes are on different chromosomes or far apart, while allelic and mutant genes refer to variants of a gene.

7. Fill in the Blanks:
Genes located on the same chromosome are called __________.
Options:
(a) Linked
(b) Unlinked
(c) Alleles
(d) Epistatic
Explanation: The correct answer is (a) Linked. These genes tend to be inherited together unless separated by recombination. Unlinked genes assort independently, alleles are alternate forms of a gene, and epistatic genes mask effects of other genes.

8. Which type of cross is used to map genes on a chromosome?
Options:
(a) Test cross
(b) Dihybrid cross
(c) Back cross
(d) Monohybrid cross
Explanation: The correct answer is (a) Test cross. Test crosses, especially with linked genes, allow calculation of recombination frequency, helping map gene positions. Dihybrid and monohybrid crosses show inheritance patterns but are less precise for mapping linked genes.

9. Single Correct Answer:
Which genetic principle fails for closely linked genes?
Options:
(a) Independent assortment
(b) Segregation
(c) Dominance
(d) Mutation
Explanation: The correct answer is (a) Independent assortment. Closely linked genes do not assort independently due to physical proximity on the same chromosome, although segregation of alleles still occurs. Dominance and mutation are unrelated to linkage effects.

10. Choose the correct statements:
(i) Linked genes are close together on the same chromosome
(ii) Recombination can separate linked genes
(iii) All linked genes follow independent assortment
(iv) Crossing over occurs during meiosis
Options:
(a) i, ii, iv
(b) i, iii, iv
(c) ii, iii
(d) i, iii
Explanation: The correct answer is (a) i, ii, iv. Linked genes are close together, recombination can separate them, and crossing over occurs in meiosis. Not all linked genes follow independent assortment, which is valid only for unlinked genes.

Topic: Mendelian Genetics
Subtopic: Autosomal and Sex-linked Traits

Keyword Definitions:
• Autosome: Any chromosome that is not a sex chromosome.
• Dominant Trait: A trait expressed in the presence of one or two alleles.
• Recessive Trait: A trait expressed only when two copies are present.
• Haemophilia: X-linked recessive bleeding disorder.
• Myotonic Dystrophy: Autosomal dominant genetic disorder affecting muscles.
• Thalassemia: Inherited blood disorder, often autosomal recessive.
• Sickle Cell Anaemia: Autosomal recessive disorder causing abnormal hemoglobin.
• Allele: Variant form of a gene.
• Gene: DNA sequence coding for a protein or trait.
• Phenotype: Observable traits of an organism.

Lead Question (2022):
Which of the following occurs due to the presence of autosome linked dominant trait?
Options:
1. Myotonic dystrophy
2. Haemophilia
3. Thalassemia
4. Sickle cell anaemia

Explanation: The correct answer is 1. Myotonic dystrophy. It is an autosomal dominant disorder, meaning a single copy of the mutant allele on an autosome is sufficient to express the disease. Haemophilia is X-linked recessive, while thalassemia and sickle cell anaemia are autosomal recessive, requiring two defective alleles for expression.

Guessed MCQs for NEET UG:

1. Which disorder is inherited in an autosomal dominant pattern?
Options:
(a) Huntington’s disease
(b) Cystic fibrosis
(c) Thalassemia
(d) Phenylketonuria
Explanation: The correct answer is (a) Huntington’s disease. It is caused by a dominant allele on an autosome, meaning a single copy of the defective gene can cause disease. In contrast, cystic fibrosis, thalassemia, and phenylketonuria are autosomal recessive disorders requiring two defective alleles.

2. Haemophilia is classified as:
Options:
(a) Autosomal dominant
(b) Autosomal recessive
(c) X-linked recessive
(d) X-linked dominant
Explanation: The correct answer is (c) X-linked recessive. Haemophilia is caused by mutations on the X chromosome and typically affects males. Autosomal dominant traits require only one defective allele, unlike haemophilia, which follows sex-linked inheritance.

3. Assertion-Reason MCQ:
Assertion (A): Sickle cell anaemia is autosomal recessive.
Reason (R): Two defective alleles are required to express the disease.
Options:
(a) Both A and R are true, R explains A
(b) Both A and R are true, R does not explain A
(c) A is true, R is false
(d) A is false, R is true
Explanation: The correct answer is (a). Sickle cell anaemia requires two defective alleles on autosomes for the disease phenotype to appear. The presence of only one allele results in a carrier state, demonstrating the recessive inheritance pattern.

4. Matching Type MCQ:
Match the disorder with its inheritance type:
List - I List - II
(a) Myotonic dystrophy (i) Autosomal recessive
(b) Haemophilia (ii) Autosomal dominant
(c) Thalassemia (iii) X-linked recessive
Options:
1. a-ii, b-iii, c-i
2. a-i, b-ii, c-iii
3. a-iii, b-i, c-ii
4. a-ii, b-i, c-iii
Explanation: The correct answer is 1. Myotonic dystrophy is autosomal dominant, Haemophilia is X-linked recessive, and Thalassemia is autosomal recessive. This classification helps understand genetic risk, inheritance patterns, and counseling for affected families.

5. Which condition requires only one defective allele to express the trait?
Options:
(a) Cystic fibrosis
(b) Myotonic dystrophy
(c) Sickle cell anaemia
(d) Tay-Sachs disease
Explanation: The correct answer is (b) Myotonic dystrophy. It is autosomal dominant; a single defective allele is sufficient to show the phenotype. Autosomal recessive conditions like cystic fibrosis, sickle cell anaemia, and Tay-Sachs require two defective alleles for disease manifestation.

6. Thalassemia is inherited as:
Options:
(a) Autosomal dominant
(b) Autosomal recessive
(c) X-linked dominant
(d) X-linked recessive
Explanation: The correct answer is (b) Autosomal recessive. Individuals must inherit two defective alleles to express the disorder. A single allele results in carrier status. Autosomal dominant disorders, like Myotonic dystrophy, require only one mutant allele for phenotype expression.

7. Fill in the Blanks:
__________ disorder manifests even if one defective allele is present.
Options:
(a) Autosomal recessive
(b) Autosomal dominant
(c) X-linked recessive
(d) X-linked dominant
Explanation: The correct answer is (b) Autosomal dominant. In such disorders, a single mutant allele on an autosome is sufficient to produce the phenotype. The presence of only one defective allele causes the disease, unlike autosomal recessive traits which require two defective copies.

8. Which of the following is X-linked?
Options:
(a) Myotonic dystrophy
(b) Haemophilia
(c) Thalassemia
(d) Sickle cell anaemia
Explanation: The correct answer is (b) Haemophilia. Haemophilia is caused by mutations on the X chromosome, affecting mostly males. Myotonic dystrophy is autosomal dominant, while thalassemia and sickle cell anaemia are autosomal recessive, inherited independently of sex chromosomes.

9. Single Correct Answer:
Which disease shows autosomal dominant inheritance and muscular symptoms?
Options:
(a) Myotonic dystrophy
(b) Huntington’s disease
(c) Thalassemia
(d) Sickle cell anaemia
Explanation: The correct answer is (a) Myotonic dystrophy. It is autosomal dominant and characterized by progressive muscle weakness and myotonia. Huntington’s disease is neurological, while thalassemia and sickle cell anaemia primarily affect blood, demonstrating distinct autosomal dominant and recessive traits.

10. Choose the correct statements:
(i) Myotonic dystrophy is autosomal dominant
(ii) Sickle cell anaemia is autosomal recessive
(iii) Haemophilia is X-linked recessive
(iv) Thalassemia is X-linked dominant
Options:
(a) i, ii, iii
(b) i, iii, iv
(c) ii, iii
(d) i, ii, iv
Explanation: The correct answer is (a) i, ii, iii. Myotonic dystrophy is autosomal dominant, Sickle cell anaemia is autosomal recessive, and Haemophilia is X-linked recessive. Thalassemia is autosomal recessive, not X-linked dominant, showing correct classification of common genetic disorders.

Topic: Mendelian Inheritance
Subtopic: Laws of Inheritance

Keyword Definitions:

• Mendel: Gregor Mendel, the father of genetics, studied inheritance in pea plants.

• Pea Plants: Pisum sativum, used by Mendel to study heredity due to easily observable traits.

• Contrasting Traits: Different forms of a character, such as tall/short or green/yellow.

• Laws of Inheritance: Principles proposed by Mendel describing how traits are transmitted from parents to offspring.

• Characters: Observable features such as seed shape, flower color, pod shape, and stem height.

Lead Question (2022)
Given below are two statements :
Statement I : Mendel studied seven pairs of contrasting traits in pea plants and proposed the Laws of Inheritance.
Statement II : Seven characters examined by Mendel in his experiment on pea plants were seed shape and colour, flower colour, pod shape and colour, flower position and stem height.
In the light of the above statements, choose the correct answer from the options given below :
(1) Both Statement I and Statement II are incorrect
(2) Statement I is correct but Statement II is incorrect
(3) Statement I is incorrect but Statement II is correct
(4) Both Statement I and Statement II are correct

Explanation:
Mendel studied seven pairs of contrasting traits in pea plants and formulated the Laws of Inheritance, including the law of segregation and independent assortment. The seven traits he examined included seed shape, seed colour, flower colour, pod shape, pod colour, flower position, and stem height. Correct answer is (4).

1. Single Correct Answer MCQ:
Which law states that alleles segregate independently during gamete formation?
(1) Law of Dominance
(2) Law of Segregation
(3) Law of Independent Assortment
(4) Law of Evolution

Explanation:
Mendel’s Law of Independent Assortment states that different allele pairs segregate independently during gamete formation, ensuring genetic variation. The law of segregation refers to separation of alleles for a single trait. Correct answer is (3).

2. Single Correct Answer MCQ:
A pea plant with round seeds (RR) is crossed with a plant with wrinkled seeds (rr). The F1 generation will have:
(1) All wrinkled seeds
(2) All round seeds
(3) 3:1 round to wrinkled
(4) 1:1 ratio

Explanation:
Crossing homozygous round (RR) with homozygous wrinkled (rr) results in F1 all heterozygous (Rr) showing the dominant round phenotype. The round trait is dominant over wrinkled. Correct answer is (2).

3. Single Correct Answer MCQ:
Which of the following is a recessive trait in Mendel’s pea plants?
(1) Round seeds
(2) Yellow seeds
(3) Wrinkled seeds
(4) Axial flowers

Explanation:
Wrinkled seed shape, green seed colour, and terminal flowers are recessive traits in Mendel’s experiments, while round seeds and yellow seeds are dominant. Correct answer is (3).

4. Single Correct Answer MCQ:
Mendel’s Law of Dominance states that:
(1) One allele may mask the effect of another
(2) Alleles segregate during gamete formation
(3) Alleles assort independently
(4) Traits blend in offspring

Explanation:
The Law of Dominance explains that in a heterozygous organism, the dominant allele masks the effect of the recessive allele. Other laws deal with segregation and independent assortment. Correct answer is (1).

5. Single Correct Answer MCQ:
The phenotype ratio of monohybrid F2 generation is typically:
(1) 1:1
(2) 3:1
(3) 9:3:3:1
(4) 2:1

Explanation:
For a monohybrid cross (Aa × Aa), the F2 generation exhibits a 3:1 ratio of dominant to recessive phenotypes. The genotypic ratio is 1:2:1. Correct answer is (2).

6. Single Correct Answer MCQ:
In Mendel’s dihybrid cross, the F2 phenotypic ratio is:
(1) 3:1
(2) 9:3:3:1
(3) 1:2:1
(4) 2:1:1

Explanation:
In a dihybrid cross (AaBb × AaBb), the F2 generation shows a phenotypic ratio of 9:3:3:1 for dominant-dominant, dominant-recessive, recessive-dominant, and recessive-recessive traits. Correct answer is (2).

7. Assertion-Reason MCQ:
Assertion (A): Mendel’s experiments on pea plants laid the foundation of genetics.
Reason (R): He used true-breeding plants and controlled crosses to study inheritance.
Options:
(1) Both A and R are correct, R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both A and R incorrect

Explanation:
Mendel’s use of true-breeding pea plants and controlled crosses allowed him to deduce the laws of inheritance, establishing modern genetics. Correct answer is (1).

8. Matching Type MCQ:
Match trait with dominant allele:
A. Seed shape — 1. Round
B. Seed colour — 2. Yellow
C. Flower position — 3. Axial
Options:
(1) A–1, B–2, C–3
(2) A–2, B–1, C–3
(3) A–1, B–3, C–2
(4) A–3, B–1, C–2

Explanation:
Mendel identified round seeds, yellow seeds, and axial flowers as dominant traits. Correct matching is A–1, B–2, C–3. Correct answer is (1).

9. Fill in the Blanks:
The father of genetics is _______.
(1) Darwin
(2) Mendel
(3) Watson
(4) Crick

Explanation:
Gregor Mendel, through experiments on pea plants, established the fundamental principles of inheritance, earning the title "Father of Genetics." Correct answer is (2).

10. Choose the Correct Statements:
(a) Mendel studied seven pairs of contrasting traits
(b) Traits segregate according to the Law of Segregation
(c) Dominant traits always blend with recessive
(d) Dihybrid cross F2 phenotypic ratio is 9:3:3:1
Options:
(1) a, b, d
(2) a and c only
(3) b and c only
(4) all of the above

Explanation:
Mendel studied seven pairs of traits (a), traits segregate independently (b), dominant traits do not blend with recessive (c is false), and dihybrid cross F2 ratio is 9:3:3:1 (d). Correct statements are a, b, d. Correct answer is (1).

Topic: Sex Determination

Subtopic: XO Type and Other Mechanisms of Sex Determination

Keyword Definitions:

• Sex Determination: The biological process by which an organism develops into a male or female based on genetic, chromosomal, or environmental factors.

• XO Type: A system where females have two X chromosomes (XX) and males have one X chromosome (XO), lacking a Y chromosome.

• Chromosomes: Thread-like DNA structures carrying hereditary information determining traits including sex.

• Drosophila: A genus of small fruit flies commonly used in genetic research, having an XY type of sex determination.

Lead Question (2022):

XO type of sex determination can be found in:

(1) Birds
(2) Grasshoppers
(3) Monkeys
(4) Drosophila

Explanation (Answer: 2)
In grasshoppers, sex is determined by the XO system. Females possess two X chromosomes (XX) while males have only one X chromosome (XO). The absence of a Y chromosome in males results in their differentiation. Thus, XO mechanism operates in grasshoppers and some insects.

1. In XO type of sex determination, males are:

(1) Homogametic
(2) Heterogametic
(3) Diploid
(4) Haploid

Explanation (Answer: 2)
Males in XO sex determination are heterogametic because they produce two types of gametes: one with an X chromosome and one without it. Females are homogametic (XX), producing only X-bearing gametes.

2. Which organism shows XY type of sex determination?

(1) Grasshopper
(2) Humans
(3) Birds
(4) Butterflies

Explanation (Answer: 2)
Humans exhibit XY type sex determination. Males have XY chromosomes while females have XX. The Y chromosome carries the SRY gene, which initiates male development during embryogenesis.

3. ZW type of sex determination occurs in:

(1) Birds
(2) Humans
(3) Grasshoppers
(4) Monkeys

Explanation (Answer: 1)
In birds, sex is determined by the ZW system. Females are heterogametic (ZW), while males are homogametic (ZZ). This system is opposite to the XY mechanism found in mammals.

4. Which of the following statements is correct for XO type mechanism?

(1) Both sexes have equal X chromosomes
(2) Males possess one X chromosome
(3) Females lack X chromosome
(4) Y chromosome determines femaleness

Explanation (Answer: 2)
In XO type, males have one X chromosome (XO) and females have two (XX). The absence of Y chromosome in males determines their sex. It is commonly seen in grasshoppers.

5. In humans, presence of Y chromosome results in:

(1) Female development
(2) Male development
(3) Intersex condition
(4) Sterility

Explanation (Answer: 2)
Y chromosome in humans carries the SRY gene responsible for initiating testes development, leading to male differentiation. Hence, its presence results in male sex determination.

6. In ZW type sex determination, females are:

(1) Homogametic
(2) Heterogametic
(3) Diploid
(4) Haploid

Explanation (Answer: 2)
In the ZW type, females are heterogametic (ZW) and males are homogametic (ZZ). The ovum determines the sex of the offspring in this system, common in birds and some reptiles.

7. Assertion-Reason Type:

Assertion (A): In grasshoppers, males are XO.
Reason (R): Presence of Y chromosome determines femaleness.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, R is false
(4) A is false, R is true

Explanation (Answer: 3)
In grasshoppers, males are XO due to absence of the second X chromosome. The Y chromosome, when present, determines maleness, not femaleness. Hence, the reason is false.

8. Matching Type:

Match the following:
A. XO type — (i) Humans
B. XY type — (ii) Grasshoppers
C. ZW type — (iii) Birds
(1) A–ii, B–i, C–iii
(2) A–iii, B–ii, C–i
(3) A–i, B–iii, C–ii
(4) A–ii, B–iii, C–i

Explanation (Answer: 1)
XO type is seen in grasshoppers, XY type in humans, and ZW type in birds. Each organism exhibits a distinct chromosomal mechanism determining male or female sex.

9. Fill in the Blanks:

In grasshoppers, females are ________ and males are ________ in chromosomal constitution.

(1) XY, XX
(2) XX, XO
(3) XO, XY
(4) ZZ, ZW

Explanation (Answer: 2)
In grasshoppers, females have two X chromosomes (XX), while males possess only one (XO). This chromosomal difference determines their sex.

10. Choose the Correct Statements:

(1) Y chromosome determines maleness in humans.
(2) XO system occurs in grasshoppers.
(3) ZW system occurs in birds.
(4) All the above.

Explanation (Answer: 4)
All statements are correct. Y chromosome determines maleness in humans, grasshoppers exhibit XO mechanism, and birds show ZW type sex determination. These mechanisms illustrate diversity in chromosomal sex determination across species.

Topic: Mendelian Genetics

Subtopic: Sickle Cell Anaemia

Keyword Definitions:

• Sickle cell anaemia Genetic disorder caused by substitution mutation in β-globin gene leading to sickle-shaped RBCs.

• Homozygous Having two identical alleles of a gene, either dominant or recessive.

• Heterozygous Having two different alleles of a gene, one dominant and one recessive.

• Progeny The offspring produced from a cross between two parents.

• Punnett square A diagram used to predict genotype and phenotype ratios in genetic crosses.

Lead Question - 2021

In a cross between a male and female, both heterozygous for sickle cell anaemia gene, what percentage of the progeny will be diseased?
(1) 75%
(2) 25%
(3) 100%
(4) 50%

Explanation: Sickle cell anaemia is autosomal recessive. Cross between heterozygous parents (AS × AS) gives 25% AA (normal), 50% AS (carrier), and 25% SS (diseased). Thus, 25% of progeny will be affected with sickle cell anaemia. Correct answer is option (2).

1. Which type of mutation causes sickle cell anaemia?
(1) Frame shift mutation
(2) Substitution mutation
(3) Deletion mutation
(4) Inversion mutation

Explanation: Sickle cell anaemia is caused by substitution of glutamic acid with valine at the sixth position of β-globin chain. It is a point mutation, specifically substitution. Therefore, the correct answer is substitution mutation.

2. A carrier individual for sickle cell anaemia has genotype:
(1) AA
(2) AS
(3) SS
(4) Aa

Explanation: Carrier individuals possess one normal allele and one defective allele for sickle cell anaemia. Their genotype is AS, where A represents normal and S represents sickle gene. Thus, the correct answer is AS.

3. Assertion (A): Heterozygous condition for sickle cell anaemia protects against malaria.
Reason (R): Sickle shaped RBCs provide an environment unfavorable for Plasmodium survival.
(1) Both A and R are true, and R explains A
(2) Both A and R are true, but R does not explain A
(3) A is true, R is false
(4) A is false, R is true

Explanation: In heterozygous condition (AS), the presence of some sickle-shaped RBCs inhibits multiplication of Plasmodium, giving partial resistance against malaria. Both Assertion and Reason are true, and Reason correctly explains Assertion. Correct answer is option (1).

4. Match the following:
A. AA - i. Normal
B. AS - ii. Carrier
C. SS - iii. Diseased
Options:
(1) A-i, B-ii, C-iii
(2) A-ii, B-i, C-iii
(3) A-iii, B-i, C-ii
(4) A-i, B-iii, C-ii

Explanation: In sickle cell anaemia, AA represents normal, AS represents carrier, and SS represents diseased condition. Hence, the correct matching is option (1).

5. Which amino acid substitution occurs in sickle cell anaemia?
(1) Glutamic acid to valine
(2) Valine to glutamic acid
(3) Alanine to valine
(4) Glycine to serine

Explanation: In sickle cell anaemia, glutamic acid at the sixth position of β-globin chain is substituted by valine. This leads to defective haemoglobin HbS. Thus, the correct answer is glutamic acid to valine.

6. Fill in the blank:
Sickle cell anaemia is an example of __________ disorder.
(1) Autosomal dominant
(2) Autosomal recessive
(3) X-linked dominant
(4) Y-linked

Explanation: Sickle cell anaemia is inherited as an autosomal recessive trait. Only individuals with SS genotype show the disease. Thus, the correct answer is autosomal recessive disorder.

7. Which of the following statements is correct for sickle cell anaemia?
(1) It is caused by frame shift mutation
(2) Heterozygotes show full disease expression
(3) Homozygotes (SS) are affected severely
(4) It is X-linked disorder

Explanation: Homozygous condition (SS) causes severe sickle cell disease, heterozygotes are carriers, and it is not X-linked. Correct answer is option (3).

8. Choose the correct statements:
(a) Sickle cell anaemia is due to substitution mutation.
(b) Heterozygous individuals are carriers.
(c) Homozygous SS individuals show the disease.
(d) It is inherited as autosomal recessive trait.
Options:
(1) a, b, c only
(2) b, c, d only
(3) a, c, d only
(4) a, b, c, d

Explanation: All given statements correctly represent features of sickle cell anaemia, including substitution mutation, carrier state in heterozygotes, disease in SS, and autosomal recessive inheritance. Thus, the correct answer is option (4).

9. What is the function of normal haemoglobin compared to HbS?
(1) Normal haemoglobin carries oxygen efficiently
(2) HbS polymerizes under low oxygen
(3) Normal haemoglobin maintains RBC shape
(4) All of these

Explanation: Normal haemoglobin ensures efficient oxygen transport and maintains biconcave RBC shape. In HbS, polymerization occurs under low oxygen, causing sickling. Hence, all statements are correct. Correct answer is option (4).

10. Which of the following clinical symptoms is typical of sickle cell anaemia?
(1) Repeated infections
(2) Anaemia and fatigue
(3) Joint pain and organ damage
(4) All of these

Explanation: Clinical symptoms of sickle cell anaemia include repeated infections, severe anaemia with fatigue, joint pain due to blocked capillaries, and progressive organ damage. Therefore, the correct answer is all of these.

Subtopic: Gene Detection and Cancer

• Mutated Gene: A gene that has undergone a change in its DNA sequence leading to abnormal function.

• Probe: A short strand of DNA or RNA labeled with a radioactive or fluorescent marker to detect complementary sequences.

• Hybridization: The process of complementary nucleic acid strands binding together.

• Complementary DNA: DNA sequence that pairs specifically with the target DNA.

• Autoradiography: Detection of radioactive molecules on a photographic film.

• Gene Clone: Identical copies of a gene created for study.

• Cancer Gene Detection: Identifying mutated genes responsible for cancer development.

• Radioactive Labeling: Tagging nucleotides or probes with radioactive isotopes for visualization.

• Hybridisation Signal: The presence of complementary DNA-probe binding detectable on film.

• Genetic Screening: Process to identify mutations in specific genes.

• DNA Complementarity: Specific base pairing between DNA strands (A-T, C-G).

Lead Question - 2021

Nowadays it is possible to detect the mutated gene causing cancer by allowing radioactive probe to hybridise its complementary DNA in a clone of cells, followed by its detection using autoradiography because:

Options:
A. Mutated gene completely and clearly appears on a photographic film
B. Mutated gene does not appear on a photographic film as the probe has no complementarity with it
C. Mutated gene does not appear on photographic film as the probe has complementarity with it
D. Mutated gene cannot be detected by hybridisation

Explanation: A radioactive probe binds to complementary DNA. If a gene is mutated, the probe may not bind due to lack of complementarity. Therefore, the mutated gene does not produce a signal on autoradiography film, allowing detection. Answer: Mutated gene does not appear on a photographic film as the probe has no complementarity with it.

1. What is the main role of a probe in gene detection?
Options:
A. To cut DNA
B. To bind complementary DNA sequences
C. To induce mutation
D. To replicate DNA

Explanation: A probe is used to bind specifically to complementary DNA sequences. This allows visualization of target genes using radioactive or fluorescent labels. Probes do not cut, mutate, or replicate DNA. Answer: To bind complementary DNA sequences.

2. Autoradiography is used for:
Options:
A. Visualizing DNA-probe binding
B. Synthesizing DNA
C. Measuring RNA levels
D. Cutting genes

Explanation: Autoradiography detects radioactive labels on probes bound to DNA, producing an image on photographic film, which shows presence or absence of target sequences. It does not synthesize DNA, measure RNA, or cut genes. Answer: Visualizing DNA-probe binding.

3. Hybridisation in molecular genetics refers to:
Options:
A. DNA replication
B. Complementary base pairing
C. Protein synthesis
D. RNA splicing

Explanation: Hybridisation occurs when single-stranded nucleic acids bind with complementary sequences. It is the basis of probe-based gene detection. Answer: Complementary base pairing.

4. Which type of label is commonly used for detecting probes?
Options:
A. Fluorescent or radioactive
B. Enzymatic only
C. Magnetic
D. None

Explanation: Probes are labeled with radioactive or fluorescent markers for visualization on films or imaging devices. Magnetic or enzymatic labels are less commonly used for traditional autoradiography. Answer: Fluorescent or radioactive.

5. A gene clone refers to:
Options:
A. Single mutated cell
B. Identical copies of a gene
C. Random DNA fragment
D. Unrelated RNA molecule

Explanation: A gene clone is a set of identical copies of a specific gene created for study. This enables hybridisation-based detection. Answer: Identical copies of a gene.

6. Which gene can be detected by a complementary radioactive probe?
Options:
A. Mutated gene with mismatches
B. Non-complementary sequence
C. Complementary target gene
D. Random DNA sequence

Explanation: Only the complementary target gene hybridizes with the probe, producing a detectable signal. Mutated or non-complementary sequences fail to bind efficiently, making them undetectable. Answer: Complementary target gene.

7. Assertion-Reason:
Assertion (A): Mutated gene may not appear on autoradiography.
Reason (R): The probe binds only to complementary sequences.
Options:
A. Both A and R are true, R is correct explanation
B. Both A and R are true, R is not correct explanation
C. A is true, R is false
D. A is false, R is true

Explanation: If the gene is mutated, complementarity is lost, preventing probe binding. Autoradiography will show absence of signal. The reason correctly explains the assertion. Answer: Both A and R are true, R is correct explanation.

8. Match the following:
Column I: 1. Probe 2. Autoradiography 3. Gene clone 4. Mutated gene
Column II: A. Detect DNA-probe binding B. Identical copies C. May not bind D. Detect complementary DNA
Options:
A. 1-D, 2-B, 3-A, 4-C
B. 1-A, 2-D, 3-C, 4-B
C. 1-D, 2-A, 3-B, 4-C
D. 1-C, 2-B, 3-D, 4-A

Explanation: Correct matching: Probe – detects complementary DNA (D), Autoradiography – detects DNA-probe binding (A), Gene clone – identical copies (B), Mutated gene – may not bind probe (C). Answer: 1-D, 2-A, 3-B, 4-C.

9. Fill in the blank: Complementary binding of probe occurs due to _______.
Options:
A. Base pairing rules
B. Random diffusion
C. Protein synthesis
D. Mutation

Explanation: Complementary binding is based on Watson-Crick base pairing rules (A-T, C-G). This ensures the probe binds specifically to target sequences. Answer: Base pairing rules.

10. Choose the correct statements:
1. Probe binds complementary DNA.
2. Autoradiography visualizes hybridization.
3. Mutated genes may fail to bind probe.
Options:
A. 1 and 2 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2, and 3

Explanation: All statements are correct. Probes bind complementary sequences, autoradiography visualizes binding, and mutations may prevent binding, allowing detection of gene changes. Answer: 1, 2, and 3.

Topic: Central Dogma of Molecular Biology
Subtopic: Replication, Transcription, Translation

Keyword Definitions:

• Replication: Process of copying DNA to form an identical DNA molecule.

• Transcription: Synthesis of RNA using DNA as a template.

• Translation: Process of protein synthesis from mRNA.

• Central Dogma: Flow of genetic information from DNA → RNA → Protein.

• Transduction: Transfer of genetic material by a virus.

Lead Question - 2021

Complete the flow chart on the central dogma.

(1) (a)-Translation; (b)-Replication; (c)-Transcription; (d)-Transduction
(2) (a)-Replication; (b)-Transcription; (c)-Translation; (d)-Protein
(3) (a)-Transduction; (b)-Translation; (c)-Replication; (d)-Protein
(4) (a)-Replication; (b)-Transcription; (c)-Transduction; (d)-Protein

Explanation: The central dogma describes the flow of genetic information as DNA replicates to form new DNA, transcribes to form RNA, and RNA translates into proteins. The correct sequence is (a)-Replication; (b)-Transcription; (c)-Translation; (d)-Protein. Therefore, the correct answer is option (2).

1) Which enzyme is responsible for unwinding the DNA helix during replication?
(1) RNA polymerase
(2) DNA helicase
(3) DNA ligase
(4) Primase

Explanation: DNA helicase is the enzyme that unwinds the double helix at the replication fork to expose the template strands for synthesis. This unwinding is essential for replication to proceed. Thus, the correct answer is option (2) DNA helicase.

2) In eukaryotes, transcription occurs in the:
(1) Cytoplasm
(2) Ribosome
(3) Nucleus
(4) Mitochondria

Explanation: In eukaryotic cells, transcription takes place inside the nucleus where DNA is located. The mRNA then exits the nucleus for translation in the cytoplasm. Hence, the correct answer is option (3) Nucleus.

3) Which of the following is not required for translation?
(1) Ribosomes
(2) tRNA
(3) mRNA
(4) DNA ligase

Explanation: Translation requires ribosomes, tRNA, and mRNA to assemble amino acids into a polypeptide chain. DNA ligase is required in replication, not in translation. Thus, the correct answer is option (4) DNA ligase.

4) In prokaryotes, replication begins at:
(1) Multiple origins
(2) A single origin
(3) The nucleus
(4) Telomeres

Explanation: Prokaryotic replication starts from a single origin of replication since their chromosomes are circular. In contrast, eukaryotic chromosomes have multiple origins. Hence, the correct answer is option (2) A single origin.

5) During transcription, the RNA strand is complementary to:
(1) Coding strand
(2) Non-coding strand
(3) Both strands
(4) Entire genome

Explanation: During transcription, the RNA strand is complementary to the DNA non-coding strand (template strand) and resembles the coding strand except for uracil in place of thymine. Thus, the correct answer is option (2) Non-coding strand.

6) Which base pairs with adenine in RNA?
(1) Thymine
(2) Uracil
(3) Cytosine
(4) Guanine

Explanation: In RNA, adenine pairs with uracil instead of thymine due to the absence of thymine in RNA nucleotides. Therefore, the correct answer is option (2) Uracil.

7) Assertion (A): DNA replication is semiconservative.
Reason (R): Each daughter DNA has one parental and one newly synthesized strand.
(1) Both A and R are true, R explains A
(2) Both A and R are true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Meselson and Stahl’s experiment proved DNA replication is semiconservative, where each new DNA molecule contains one parental and one new strand. Hence, both A and R are true, and R explains A. Correct answer is option (1).

8) Match the following:
(a) Okazaki fragments - (i) Lagging strand
(b) Promoter region - (ii) Initiation of transcription
(c) Ribosome - (iii) Protein synthesis
(d) Splicing - (iv) Removal of introns
Options:
(1) (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
(2) (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
(3) (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
(4) (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Explanation: Okazaki fragments are short DNA pieces on the lagging strand, the promoter initiates transcription, ribosomes perform protein synthesis, and splicing removes introns from pre-mRNA. The correct matching is option (1).

9) Fill in the blank: The enzyme that adds RNA primers during replication is called ______.
(1) DNA polymerase
(2) Primase
(3) Helicase
(4) Topoisomerase

Explanation: Primase synthesizes short RNA primers that serve as starting points for DNA polymerase to extend DNA strands. Without primers, DNA polymerase cannot initiate synthesis. Hence, the correct answer is option (2) Primase.

10) Choose the correct statements:
A. Exons are coding sequences.
B. Introns are non-coding sequences removed during RNA processing.
C. tRNA carries amino acids to ribosomes.
D. rRNA serves as a template for protein synthesis.
Options:
(1) A, B, C correct
(2) B, C, D correct
(3) A, C, D correct
(4) A, B, D correct

Explanation: Exons are coding sequences, introns are spliced out, and tRNA carries amino acids during translation. rRNA, however, is not a template but a structural component of ribosomes. Therefore, correct statements are A, B, and C. The answer is option (1).

Topic: Mendelian Genetics
Subtopic: Punnett Square and Inheritance Patterns

Keyword Definitions:

• Gametes: Haploid reproductive cells produced by parents through meiosis, containing a single set of chromosomes.

• Zygote: Diploid cell formed by the fusion of male and female gametes during fertilization.

• F1 Generation: First filial generation resulting from a cross between parent plants.

• F2 Generation: Second filial generation obtained by selfing or crossing F1 individuals.

• Punnett Square: Diagrammatic tool used to predict genotypic and phenotypic ratios in offspring from a genetic cross.

• Genotype: Genetic constitution of an organism represented by allele combinations.

• Phenotype: Observable characteristics of an organism influenced by genotype and environment.

• Mendelian Inheritance: Pattern of inheritance first described by Gregor Mendel involving dominant and recessive alleles.

Lead Question - 2021

The production of gametes by the parents, formation of zygotes, the F1 and F2 plants, can be understood from a diagram called:
(1) Punch square
(2) Punnett square
(3) Net square
(4) Bullet square

Explanation: The correct answer is (2) Punnett square. This diagram represents all possible combinations of gametes from two parents, predicting genotypic and phenotypic ratios in F1 and F2 generations. It illustrates Mendelian inheritance, showing how dominant and recessive alleles segregate during gamete formation and fertilization.

Guessed Questions:

1) Single Correct Answer: The F2 generation in Mendelian crosses results from:
(1) Cross between parents
(2) Selfing of F1 plants
(3) Random mutation
(4) Environmental influence

Explanation: The correct answer is (2) Selfing of F1 plants. F2 generation is obtained by allowing F1 individuals to self-fertilize or intercross. This allows segregation of alleles according to Mendel’s laws, revealing phenotypic ratios like 3:1 for monohybrid crosses.

2) Single Correct Answer: The diagrammatic representation of gamete combination is:
(1) Flowchart
(2) Punnett square
(3) Pie chart
(4) Venn diagram

Explanation: The correct answer is (2) Punnett square. It helps visualize gamete combinations and predicts genotypic and phenotypic outcomes. Each parent’s gametes are arranged on the sides, and their combinations in the boxes show possible zygotes in F1 or F2 generations.

3) Single Correct Answer: In a monohybrid Punnett square, the genotypic ratio in F2 is typically:
(1) 1:2:1
(2) 3:1
(3) 9:3:3:1
(4) 1:1

Explanation: The correct answer is (1) 1:2:1. In F2 of a monohybrid cross, genotypes appear as one homozygous dominant, two heterozygous, and one homozygous recessive, predicted by Punnett square, illustrating Mendel’s principle of segregation.

4) Assertion (A): Punnett square predicts offspring traits.
Reason (R): It shows gamete combinations from parents.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). Punnett square demonstrates all possible combinations of gametes from two parents. By mapping these combinations, it predicts the genotypes and phenotypes of offspring, helping to understand inheritance patterns and Mendelian ratios in F1 and F2 generations.

5) Single Correct Answer: Phenotype of offspring is influenced by:
(1) Only environment
(2) Only genotype
(3) Genotype and environment
(4) Gamete shape

Explanation: The correct answer is (3) Genotype and environment. Punnett square predicts genotype, but observable traits (phenotype) result from interaction of genetic makeup and environmental factors. Both F1 and F2 generations show phenotypic variations based on this interaction.

6) Single Correct Answer: A dihybrid Punnett square has how many boxes?
(1) 2
(2) 4
(3) 16
(4) 8

Explanation: The correct answer is (3) 16. In a dihybrid cross, each parent produces four types of gametes. Arranging these in a 4x4 Punnett square results in 16 boxes, representing all possible genotype combinations and allowing prediction of a 9:3:3:1 phenotypic ratio in F2.

7) Matching Type: Match generation with description.
List-I    List-II
(a) P generation    (i) Parent plants
(b) F1 generation    (ii) First filial generation
(c) F2 generation    (iii) Second filial generation
(d) Gametes    (iv) Haploid reproductive cells

Explanation: Correct answer: (a) i, (b) ii, (c) iii, (d) iv. P generation is parents, F1 is first generation offspring, F2 is second generation, and gametes are haploid cells. Punnett square predicts combinations of gametes to produce F1 and F2 genotypes and phenotypes.

8) Single Correct Answer: Punnett square illustrates:
(1) Chromosome structure
(2) Gamete combinations and inheritance
(3) Cell division stages
(4) Enzyme activity

Explanation: The correct answer is (2) Gamete combinations and inheritance. Punnett square systematically shows possible zygote genotypes from parent gametes. It is widely used to predict outcomes of monohybrid and dihybrid crosses in F1 and F2 generations.

9) Fill in the blank: The Punnett square helps predict _______ of offspring.
(1) Genotype and phenotype
(2) Only genotype
(3) Only phenotype
(4) Number of gametes

Explanation: The correct answer is (1) Genotype and phenotype. Punnett square shows how parental alleles combine in gametes, predicting both genetic constitution and observable traits of F1 and F2 offspring according to Mendelian principles.

10) Choose the correct statements:
(a) Punnett square predicts F1 and F2 outcomes.
(b) It illustrates gamete combinations.
(c) F2 generation is obtained by selfing F1.
(d) Gametes are diploid cells.
Options:
(1) a, b, c
(2) a, c, d
(3) b, c, d
(4) All are correct

Explanation: The correct answer is (1) a, b, c. Punnett square predicts outcomes for F1 and F2, illustrates gamete combinations, and F2 results from selfing or crossing F1 plants. Gametes are haploid, not diploid, so option (d) is incorrect.

Subtopic: Induced Mutations

Keyword Definitions:

• Mutation: A permanent change in DNA sequence, leading to altered traits.

• Mutagen: An agent like radiation or chemical that induces mutations.

• Gamma rays: High-energy ionizing radiation capable of inducing mutations in plants.

• Infrared rays: Low-energy radiation producing heat, not effective as mutagens.

• Zeatin: A naturally occurring cytokinin plant hormone promoting cell division.

• Kinetin: A synthetic cytokinin used in tissue culture to stimulate growth.

• Induced mutation: Mutation artificially created using radiation or chemicals for crop improvement.

Lead Question - 2021

Mutations in plant cells can be induced by:
(1) Infrared rays
(2) Gamma rays
(3) Zeatin
(4) Kinetin

Explanation: The correct answer is (2) Gamma rays. They are powerful ionizing radiations that can break DNA strands and induce heritable mutations. This principle is widely applied in mutation breeding to develop new crop varieties. Infrared rays and cytokinins like zeatin or kinetin do not induce mutations.

Guessed Questions:

1) Which radiation is most effective in mutation breeding?
(1) UV radiation
(2) Infrared radiation
(3) Gamma radiation
(4) Visible light

Explanation: The correct answer is (3) Gamma radiation. It penetrates deeply into plant tissues, causing double-strand breaks in DNA. This mutagenic property is harnessed in developing new crop varieties. UV has limited penetration, while infrared and visible light lack sufficient energy to alter genetic material significantly.

2) Zeatin is classified as:
(1) Auxin
(2) Gibberellin
(3) Cytokinin
(4) Abscisic acid

Explanation: The correct answer is (3) Cytokinin. Zeatin was the first naturally occurring cytokinin discovered in maize kernels. It promotes cell division and growth, regulates shoot initiation in tissue culture, and delays leaf senescence. Unlike mutagens, it cannot cause genetic changes but supports controlled growth responses in plants.

3) Kinetin is widely used in plant biotechnology for:
(1) Inducing mutations
(2) Stimulating root elongation
(3) Breaking seed dormancy
(4) Tissue culture growth

Explanation: The correct answer is (4) Tissue culture growth. Kinetin is a synthetic cytokinin promoting cell division and shoot proliferation in vitro. It does not induce mutations but regulates plant tissue development. Along with auxins, kinetin is vital in micropropagation and plant regeneration studies.

4) Which radiation is non-ionizing but still mutagenic?
(1) UV rays
(2) Gamma rays
(3) X-rays
(4) Infrared rays

Explanation: The correct answer is (1) UV rays. Though non-ionizing, UV radiation causes thymine dimers in DNA, leading to replication errors and mutations. Gamma rays and X-rays are ionizing, while infrared rays mainly produce heat and lack mutagenic potential. UV is often used in microbial mutagenesis studies.

5) Induced mutations are useful in agriculture for:
(1) Increasing seed dormancy
(2) Developing new crop varieties
(3) Reducing plant diversity
(4) Eliminating cytokinins

Explanation: The correct answer is (2) Developing new crop varieties. Induced mutations through radiation or chemicals create genetic variability, which breeders utilize to improve crop yield, disease resistance, or stress tolerance. This technique expands biodiversity instead of reducing it, providing beneficial traits to agriculture.

6) Which of the following is not a mutagen?
(1) EMS (ethyl methane sulfonate)
(2) X-rays
(3) Kinetin
(4) Gamma rays

Explanation: The correct answer is (3) Kinetin. EMS, X-rays, and gamma rays induce genetic mutations by altering DNA. Kinetin, a plant cytokinin, regulates cell growth but does not induce DNA alterations. This makes it unsuitable for mutation breeding, though useful in tissue culture studies.

7) Assertion (A): Gamma rays are used for mutation breeding in plants.
Reason (R): They cause chromosomal aberrations and genetic variations.
(1) Both A and R are true, R explains A
(2) Both A and R are true, R does not explain A
(3) A is true, R is false
(4) A is false, R is true

Explanation: The correct answer is (1) Both A and R are true, R explains A. Gamma rays induce mutations by damaging DNA and chromosomes, leading to genetic variability. Plant breeders exploit this variability to create superior crop varieties with improved yield, disease resistance, or stress tolerance.

8) Match the following:
A. Gamma rays - (i) Mutation breeding
B. Zeatin - (ii) Natural cytokinin
C. Kinetin - (iii) Synthetic cytokinin
D. EMS - (iv) Chemical mutagen
Options:
(1) A-i, B-ii, C-iii, D-iv
(2) A-ii, B-i, C-iv, D-iii
(3) A-iii, B-iv, C-ii, D-i
(4) A-iv, B-iii, C-i, D-ii

Explanation: The correct answer is (1) A-i, B-ii, C-iii, D-iv. Gamma rays are used in mutation breeding, zeatin is a natural cytokinin, kinetin is synthetic, and EMS is a potent chemical mutagen. Each has distinct applications in plant biotechnology and genetics research.

9) Fill in the blank: __________ is a chemical mutagen often used in crop improvement programs.
(1) ATP
(2) EMS
(3) Kinetin
(4) Zeatin

Explanation: The correct answer is (2) EMS. Ethyl methane sulfonate (EMS) is an alkylating chemical mutagen that induces point mutations in DNA. It is extensively used in mutation breeding programs to generate variability in crops, leading to new cultivars with desirable traits.

10) Choose the correct statements:
A. Gamma rays are ionizing radiation.
B. Kinetin is a mutagen used in breeding.
C. Zeatin is a cytokinin promoting cell division.
D. EMS is a chemical mutagen.
Options:
(1) A and B
(2) A, C and D
(3) B and C
(4) A and D

Explanation: The correct answer is (2) A, C and D. Gamma rays are ionizing mutagens, zeatin is a natural cytokinin promoting growth, and EMS is a chemical mutagen. Statement B is incorrect because kinetin is not a mutagen but a growth regulator used in tissue culture.

Subtopic: Pleiotropy

Keyword Definitions:

• Pleiotropy: A single gene affecting multiple phenotypic traits.

• Phenylketonuria (PKU): Genetic disorder due to mutation in PAH gene, causing multiple effects including intellectual disability and pigmentation changes.

• Skin color: Polygenic trait influenced by multiple genes.

• Colour blindness: X-linked trait affecting vision, typically not pleiotropic.

• ABO Blood group: Determined by a single gene, but generally not pleiotropic.

• Gene: Unit of heredity that controls a trait.

• Phenotype: Observable characteristics of an organism.

• Mutation: Change in DNA sequence affecting gene function.

Lead Question - 2020 (COVID Reexam)

The best example for pleiotropy is:

1. Skin color
2. Phenylketonuria
3. Colour Blindness
4. ABO Blood group

Explanation: Phenylketonuria is a classic example of pleiotropy, where mutation in a single PAH gene affects multiple traits including mental development, pigmentation, and metabolism. Skin color is polygenic, color blindness is X-linked, and ABO blood group affects blood type only. Correct answer: Option 2.

1. Single Correct Answer MCQ:

Which trait is influenced by a single gene but multiple effects?
1. PKU
2. Height
3. Eye color
4. Hair texture

Explanation: PKU is controlled by one gene, but it produces multiple phenotypic effects like intellectual disability and pigmentation changes, exemplifying pleiotropy. Height and eye color are polygenic, hair texture controlled by fewer genes but not pleiotropic. Answer: Option 1.

2. Single Correct Answer MCQ:

Which inheritance pattern describes PKU effects?
1. Monogenic pleiotropy
2. Polygenic
3. X-linked
4. Codominant

Explanation: PKU is monogenic pleiotropy, a single gene affecting multiple traits. Polygenic traits involve multiple genes, X-linked traits are on X chromosome, codominant traits express both alleles simultaneously. Answer: Option 1.

3. Single Correct Answer MCQ:

Which condition is not pleiotropic?
1. PKU
2. Sickle cell anemia
3. Skin color
4. Tay-Sachs disease

Explanation: Skin color is polygenic and not pleiotropic. PKU, sickle cell anemia, and Tay-Sachs show pleiotropy where one gene influences multiple traits. Answer: Option 3.

4. Single Correct Answer MCQ:

A single mutation in PAH gene causes:
1. PKU only
2. Multiple metabolic and phenotypic effects
3. Color blindness
4. ABO blood group change

Explanation: Mutation in PAH gene leads to PKU, causing multiple effects like high phenylalanine levels, intellectual disability, and pigmentation changes. This is an example of pleiotropy. Color blindness and ABO group changes are unrelated. Answer: Option 2.

5. Single Correct Answer MCQ:

Which blood group trait is not pleiotropic?
1. ABO
2. PKU
3. Sickle cell
4. Tay-Sachs

Explanation: ABO blood group is determined by a single gene affecting blood type only, without multiple phenotypic effects, thus not pleiotropic. PKU, sickle cell, Tay-Sachs demonstrate pleiotropy. Answer: Option 1.

6. Single Correct Answer MCQ:

Sickle cell anemia demonstrates pleiotropy because:
1. One gene affects red blood cells, pain, and organ damage
2. Multiple genes control anemia
3. Only hemoglobin is affected
4. It is X-linked

Explanation: Sickle cell anemia is pleiotropic as mutation in one gene affects red blood cell shape, causes pain crises, and organ damage. Multiple genes are not involved, hemoglobin alone is insufficient, and it is not X-linked. Answer: Option 1.

7. Assertion-Reason MCQ:

Assertion (A): PKU is an example of pleiotropy.
Reason (R): Mutation in a single gene causes multiple phenotypic effects.
1. Both A and R true, R correct explanation
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: PKU illustrates pleiotropy as a single PAH gene mutation leads to intellectual disability, pigmentation changes, and metabolic effects. Both assertion and reason are correct, with reason explaining the assertion. Answer: Option 1.

8. Matching Type MCQ:

Column I    Column II
(a) PKU    (i) Blood group
(b) ABO    (ii) Intellectual disability, pigmentation
(c) Colour blindness    (iii) X-linked trait
(d) Skin color    (iv) Polygenic trait

1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
3. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
4. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Explanation: PKU causes multiple effects (pleiotropy), ABO determines blood group, colour blindness is X-linked, skin color is polygenic. Correct matching: (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv). Answer: Option 1.

9. Fill in the blanks:

________ is a classic example of pleiotropy caused by a single gene mutation.
1. ABO blood group
2. Phenylketonuria
3. Skin color
4. Eye color

Subtopic: Mendel’s Experiments on Pea Plants

Keyword Definitions:

• Mendel: Father of genetics who studied inheritance patterns in pea plants.

• Contrasting characters: Pairs of traits with opposite forms, e.g., tall vs. dwarf.

• Pea plants: Pisum sativum used by Mendel for controlled hybridization experiments.

• Monohybrid cross: Cross involving a single contrasting character.

• Dihybrid cross: Cross involving two contrasting characters.

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable trait of an organism.

• Inheritance: Transmission of traits from parents to offspring.

Lead Question - 2020 (COVID Reexam)

The number of contrasting characters studied by Mendel for his experiments was:

1. 14
2. 4
3. 2
4. 7

Explanation: Mendel studied 7 contrasting characters in pea plants, each with two opposite forms, such as tall vs. dwarf and round vs. wrinkled seeds. These characters formed the basis of his monohybrid and dihybrid crosses, establishing foundational laws of inheritance. Correct answer: Option 4.

1. Single Correct Answer MCQ:

Which trait is not a Mendelian contrasting character?
1. Tall vs. dwarf
2. Yellow vs. green seeds
3. Winged vs. wingless pea
4. Round vs. wrinkled seeds

Explanation: Mendel studied seven pairs of contrasting characters in pea plants. Winged vs. wingless is not among them. Tall/dwarf, yellow/green seeds, and round/wrinkled seeds are correct examples. Answer: Option 3.

2. Single Correct Answer MCQ:

Monohybrid cross involves:
1. One contrasting character
2. Two contrasting characters
3. All characters
4. Sex-linked traits

Explanation: A monohybrid cross studies inheritance of a single contrasting character, e.g., tall vs. dwarf. Dihybrid crosses involve two characters. Sex-linked traits are a separate concept. Answer: Option 1.

3. Single Correct Answer MCQ:

Dihybrid cross studies:
1. One character
2. Two characters
3. Four characters
4. Multiple unrelated species

Explanation: Dihybrid cross involves two contrasting characters, e.g., seed shape and seed color, to study independent assortment. Monohybrid cross studies one character. Answer: Option 2.

4. Single Correct Answer MCQ:

Mendel’s pea plant experiments helped establish:
1. Laws of genetics
2. DNA structure
3. Chromosome number
4. Mutation theory

Explanation: Mendel’s experiments on seven contrasting characters established laws of segregation and independent assortment. DNA structure, chromosome numbers, and mutation theory were discovered later. Answer: Option 1.

5. Single Correct Answer MCQ:

Which seed trait is a contrasting character studied by Mendel?
1. Smooth vs. wrinkled
2. Round vs. angular
3. Black vs. white
4. Long vs. short pods

Explanation: Mendel studied seed shape: round vs. wrinkled. Other options are incorrect or not among his seven contrasting characters. Answer: Option 1.

6. Single Correct Answer MCQ:

Which is a flower color contrasting character?
1. White vs. purple
2. Yellow vs. green
3. Round vs. wrinkled
4. Tall vs. dwarf

Explanation: Flower color contrasting character in Mendel’s experiments is white vs. purple. Yellow/green and round/wrinkled relate to seeds, tall/dwarf to plant height. Answer: Option 1.

7. Assertion-Reason MCQ:

Assertion (A): Mendel studied 7 contrasting characters.
Reason (R): Each contrasting character had two opposite forms.
1. Both A and R true, R correct explanation
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Mendel selected seven contrasting characters, each with two forms like tall/dwarf, round/wrinkled. This allowed him to establish laws of inheritance. Both assertion and reason are true, with the reason correctly explaining the assertion. Answer: Option 1.

8. Matching Type MCQ:

Column I    Column II
(a) Seed color    (i) Round vs. wrinkled
(b) Seed shape    (ii) Yellow vs. green
(c) Pod shape    (iii) Inflated vs. constricted
(d) Plant height    (iv) Tall vs. dwarf

1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
3. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
4. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Explanation: Seed color: yellow vs. green, seed shape: round vs. wrinkled, pod shape: inflated vs. constricted, plant height: tall vs. dwarf. Correct matching: (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv). Answer: Option 1.

9. Fill in the blanks:

Mendel selected ______ contrasting characters in pea plants.
1. 4
2. 7
3. 14
4. 2

Explanation: Mendel selected seven pairs of contrasting characters, such as plant height and seed shape, to study inheritance and formulate laws of segregation and independent assortment. Answer: Option 2.

10. Choose correct statements:

(a) Mendel studied 7 contrasting characters
(b) Each contrasting character had two forms
(c) Pea plants were suitable for controlled hybridization
(d) Mendel discovered chromosomes

1. a, b, c only
2. a and d only
3. b and d only
4. All statements correct

Explanation: Mendel studied 7 contrasting characters, each with two forms, and pea plants allowed controlled hybridization. He did not discover chromosomes. Correct statements: a, b, c only. Answer:

Topic: Human Genetic Disorders

Subtopic: Inheritance Patterns

Keyword Definitions:

• Sickle cell anaemia – A genetic blood disorder caused by a mutation in the beta-globin gene leading to crescent-shaped red blood cells; inherited as autosomal recessive.

• Thalassemia – A group of inherited blood disorders caused by mutations in globin genes resulting in defective hemoglobin; inheritance is usually autosomal recessive.

• Haemophilia – A bleeding disorder caused by deficiency of clotting factors, usually inherited as X-linked recessive.

• Phenylketonuria (PKU) – An autosomal recessive metabolic disorder caused by mutation in the PAH gene, leading to accumulation of phenylalanine.

• Autosomal dominant – A pattern of inheritance where one copy of the mutated gene is sufficient to cause the disorder.

• Autosomal recessive – A pattern of inheritance where two copies of the mutated gene are required to express the disorder.

• X-linked – Disorders caused by genes located on the X chromosome, usually affecting males more severely.

• Y-linked – Disorders caused by genes located on the Y chromosome, inherited strictly from father to son.

• Chromosome II – Refers to the second pair of autosomes in humans, containing various genes including beta-globin for sickle cell anaemia.

• Mutation – A permanent change in the DNA sequence of a gene that may cause a genetic disorder.

• Inheritance pattern – The manner in which a genetic trait or disorder is transmitted from one generation to the next.

Lead Question - 2020

Select the correct match:
(1) Sickle cell anaemia – Autosomal recessive trait, chromosome-II
(2) Thalassemia – X linked
(3) Haemophilia – Y linked
(4) Phenylketonuria – Autosomal dominant trait

Explanation: Sickle cell anaemia is an autosomal recessive disorder caused by a mutation in the beta-globin gene on chromosome 11 (autosome II). Thalassemia is also autosomal recessive. Haemophilia is X-linked recessive, and PKU is autosomal recessive. Correct answer is (1).

1. Single Correct Answer: Which disorder is inherited as X-linked recessive?
(1) Sickle cell anaemia
(2) Thalassemia
(3) Haemophilia
(4) Phenylketonuria

Explanation: Haemophilia is caused by mutations in clotting factor genes on the X chromosome and is inherited as X-linked recessive. Males are predominantly affected. Correct answer is (3) Haemophilia.

2. Single Correct Answer: PKU is inherited in which pattern?
(1) Autosomal dominant
(2) Autosomal recessive
(3) X-linked
(4) Y-linked

Explanation: Phenylketonuria (PKU) is caused by a mutation in the PAH gene and is inherited in an autosomal recessive manner. Both parents must carry the defective gene. Correct answer is (2) Autosomal recessive.

3. Single Correct Answer: Sickle cell anaemia affects which part of the cell?
(1) White blood cells
(2) Red blood cells
(3) Platelets
(4) Plasma proteins

Explanation: Sickle cell anaemia affects red blood cells, causing them to assume a crescent shape due to abnormal hemoglobin S. This leads to anemia and vaso-occlusive crises. Correct answer is (2) Red blood cells.

4. Assertion-Reason:
Assertion (A): Thalassemia is inherited in an autosomal manner.
Reason (R): It involves mutations in globin genes located on autosomes.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Thalassemia is an autosomal recessive disorder because the globin gene mutations are located on autosomes. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer is (1).

5. Single Correct Answer: Which disorder is caused by mutation on chromosome II (11)?
(1) Thalassemia
(2) Haemophilia
(3) Sickle cell anaemia
(4) Phenylketonuria

Explanation: Sickle cell anaemia is caused by a mutation in the beta-globin gene located on chromosome 11 (autosome II). Correct answer is (3) Sickle cell anaemia.

6. Single Correct Answer: Which disease involves abnormal hemoglobin synthesis?
(1) Haemophilia
(2) Thalassemia
(3) PKU
(4) Cystic fibrosis

Explanation: Thalassemia involves reduced or absent synthesis of one of the globin chains of hemoglobin, leading to anemia. Correct answer is (2) Thalassemia.

7. Matching Type: Match the disorder with chromosome:
a. Sickle cell anaemia – i. X chromosome
b. Haemophilia – ii. Chromosome II (11)
c. PKU – iii. Chromosome 12
d. Thalassemia – iv. Chromosome 16
(1) a-ii, b-i, c-iii, d-iv
(2) a-iii, b-ii, c-i, d-iv
(3) a-iv, b-iii, c-ii, d-i
(4) a-i, b-ii, c-iv, d-iii

Explanation: Sickle cell anaemia – chromosome 11 (a-ii), Haemophilia – X chromosome (b-i), PKU – chromosome 12 (c-iii), Thalassemia – chromosome 16 (d-iv). Correct answer is (1).

8. Fill in the blank: Haemophilia is inherited as ______.
(1) Autosomal dominant
(2) Autosomal recessive
(3) X-linked recessive
(4) Y-linked

Explanation: Haemophilia is caused by mutations in genes on the X chromosome and is inherited as X-linked recessive. Correct answer is (3) X-linked recessive.

9. Single Correct Answer: Which disorder requires both parents to be carriers for a child to be affected?
(1) Haemophilia
(2) Sickle cell anaemia
(3) Y-linked disorders
(4) X-linked dominant disorders

Explanation: Autosomal recessive disorders like sickle cell anaemia require both parents to be carriers of the mutant gene for a child to express the disorder. Correct answer is (2) Sickle cell anaemia.

10. Choose the correct statements:
(a) PKU is autosomal recessive
(b) Sickle cell anaemia is X-linked
(c) Haemophilia is X-linked recessive
(d) Thalassemia is autosomal recessive
(1) a, c, d
(2) a, b, c
(3) b, c, d
(4) All of the above

Topic: Chromosomal Theory of Inheritance

Subtopic: Experimental Verification

Keyword Definitions:

• Chromosomal Theory of Inheritance – Concept stating that genes are located on chromosomes, which are the carriers of hereditary information.

• Experimental Verification – Process of confirming a scientific theory through controlled experiments.

• Boveri – German biologist who proposed that chromosomes carry genetic material essential for development.

• Morgan – American geneticist who confirmed the chromosomal theory using Drosophila experiments, linking specific genes to specific chromosomes.

• Mendel – Austrian monk who formulated laws of inheritance based on pea plant experiments, foundational for genetics.

• Sutton – American cytologist who independently proposed that chromosomes are the basis of Mendelian inheritance.

Lead Question - 2020

Experimental verification of the chromosomal theory of inheritance was done by:
(1) Boveri
(2) Morgan
(3) Mendel
(4) Sutton

Explanation: Thomas Hunt Morgan experimentally verified the chromosomal theory of inheritance by using Drosophila melanogaster, linking specific traits to specific chromosomes. His experiments provided the first direct evidence that genes are located on chromosomes. Correct answer is (2) Morgan.

1. Single Correct Answer: Who proposed that chromosomes carry genetic material essential for development?
(1) Boveri
(2) Morgan
(3) Mendel
(4) Sutton

Explanation: Boveri suggested that chromosomes carry genetic material necessary for proper development, laying the foundation for chromosomal theory. Correct answer is (1) Boveri.

2. Single Correct Answer: Who formulated the fundamental laws of inheritance?
(1) Sutton
(2) Morgan
(3) Mendel
(4) Boveri

Explanation: Mendel formulated the laws of inheritance based on pea plant experiments, establishing the principles of dominant and recessive traits. Correct answer is (3) Mendel.

3. Single Correct Answer: Who independently proposed that chromosomes are the basis of Mendelian inheritance?
(1) Sutton
(2) Morgan
(3) Mendel
(4) Boveri

Explanation: Sutton proposed that chromosomes behave according to Mendelian principles, connecting cytology with genetics. Correct answer is (1) Sutton.

4. Assertion-Reason:
Assertion (A): Morgan verified that genes are located on chromosomes.
Reason (R): He used Drosophila melanogaster for his experiments.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Morgan demonstrated that specific genes are linked to specific chromosomes using Drosophila, making both assertion and reason true and the reason explains the assertion. Correct answer is (1).

5. Single Correct Answer: Which organism was primarily used by Morgan for genetic experiments?
(1) Pea plant
(2) Fruit fly (Drosophila)
(3) Mouse
(4) Bacterium

Explanation: Morgan used Drosophila melanogaster (fruit fly) for experiments because of its short life cycle and observable mutations, enabling the mapping of genes on chromosomes. Correct answer is (2) Fruit fly.

6. Single Correct Answer: Sutton’s contribution to genetics was:
(1) Verified Mendel’s laws experimentally
(2) Proposed chromosomes as carriers of genetic material
(3) Discovered Drosophila mutations
(4) Developed hybrid pea plants

Explanation: Sutton proposed that chromosomes are the physical carriers of genes, aligning cytology with Mendelian genetics. Correct answer is (2).

7. Matching Type: Match scientists with their contribution:
a. Boveri – i. Chromosomes carry genetic material
b. Morgan – ii. Experimental verification with Drosophila
c. Mendel – iii. Laws of inheritance
d. Sutton – iv. Chromosomes as basis of Mendelian inheritance
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-iii, b-iv, c-i, d-ii
(4) a-iv, b-iii, c-ii, d-i

Explanation: Boveri proposed chromosomes carry genetic material (a-i), Morgan verified genes on chromosomes using Drosophila (b-ii), Mendel formulated laws of inheritance (c-iii), and Sutton proposed chromosomes as basis of Mendelian inheritance (d-iv). Correct answer is (1).

8. Fill in the blank: The chromosomal theory of inheritance was experimentally verified by _______.
(1) Boveri
(2) Morgan
(3) Mendel
(4) Sutton

Explanation: Thomas Hunt Morgan provided experimental proof for the chromosomal theory of inheritance using Drosophila, confirming that genes reside on chromosomes. Correct answer is (2) Morgan.

9. Single Correct Answer: Which scientist laid the theoretical foundation for chromosomal theory?
(1) Boveri
(2) Morgan
(3) Mendel
(4) Sutton

Explanation: Boveri proposed that chromosomes carry essential genetic material and are crucial for development, forming the theoretical basis of chromosomal inheritance. Correct answer is (1) Boveri.

10. Choose the correct statements:
(a) Mendel formulated laws of inheritance
(b) Morgan verified genes on chromosomes experimentally
(c) Sutton proposed chromosomes as the basis of Mendelian inheritance
(d) Boveri suggested chromosomes carry genetic material
(1) a, b, c, d
(2) a, c
(3) b, d
(4) a, b, c

Explanation: All four statements are correct: Mendel formulated inheritance laws (a), Morgan experimentally verified genes on chromosomes (b), Sutton linked chromosomes to Mendelian inheritance (c), and Boveri proposed chromosomes carry genetic material (d). Correct answer is (1) a, b, c, d.

Topic: Mendelian Inheritance

Subtopic: Mendel’s Experimental Materials

Keyword Definitions:

• True breeding: Plants that consistently produce offspring with the same traits when self-pollinated.

• Contrasting traits: Alternative forms of a character, such as tall vs. dwarf.

• Pea plant: Experimental organism chosen by Mendel for genetic studies due to clear traits and ease of breeding.

• Mendelian inheritance: Principles of heredity based on segregation and independent assortment.

• Character: Observable feature of an organism controlled by genes.

• Trait: Variants of a character, for example, purple or white flower color.

Lead Question - 2020

How many true breeding pea plant varieties did Mendel select as pairs, which were similar except in one character with contrasting traits?

(1) 14
(2) 8
(3) 4
(4) 2

Explanation: The correct answer is (1) 14. Mendel selected 14 true-breeding pea plant varieties representing seven contrasting pairs of traits. Each pair differed only in one character, such as tall/dwarf or round/wrinkled seeds. These true-breeding lines provided the foundation for establishing Mendel’s laws of inheritance through systematic crossing experiments.

1. Mendel chose pea plants because:
(1) They were tall plants
(2) They had easily observable traits
(3) They needed less water
(4) They were rare
Explanation: The correct answer is (2). Pea plants were ideal because they had clear contrasting traits, short generation time, ability for both self and cross-pollination, and were easy to cultivate. These factors allowed Mendel to obtain reliable experimental results and establish the basic principles of heredity that are still followed today.

2. Which of the following was not a contrasting trait studied by Mendel?
(1) Tall vs. dwarf
(2) Yellow vs. green seed
(3) Red vs. white flower
(4) Round vs. wrinkled seed
Explanation: The correct answer is (3) Red vs. white flower. Mendel studied seven traits, including stem height, seed color, seed shape, pod shape, pod color, flower position, and flower color (purple vs. white). Red vs. white was not among the traits he selected, hence it is incorrect for Mendelian studies.

3. In Mendel’s experiments, purple flower color is:
(1) Dominant
(2) Recessive
(3) Codominant
(4) Incomplete dominant
Explanation: The correct answer is (1) Dominant. In pea plants, purple flower color dominates over white. When a purple-flowered plant was crossed with a white-flowered plant, the F1 generation expressed only purple flowers, showing the principle of dominance. White flower color appeared again in the F2 generation with a 3:1 ratio.

4. Which ratio did Mendel observe in the F2 generation of monohybrid crosses?
(1) 1:1
(2) 3:1
(3) 9:3:3:1
(4) 2:1
Explanation: The correct answer is (2) 3:1. Mendel found that in monohybrid crosses, the F2 generation showed dominant to recessive traits in a 3:1 ratio. This observation supported the law of segregation, proving that factors (genes) segregate during gamete formation and recombine during fertilization without blending.

5. Which principle was derived from dihybrid crosses?
(1) Law of segregation
(2) Law of independent assortment
(3) Law of dominance
(4) Law of blending inheritance
Explanation: The correct answer is (2). Dihybrid crosses revealed the law of independent assortment, which states that different gene pairs assort independently during gamete formation. Mendel demonstrated this by crossing plants differing in two traits, such as seed shape and seed color, producing a 9:3:3:1 phenotypic ratio in the F2 generation.

6. Which plant structure enabled controlled pollination in Mendel’s experiments?
(1) Stigma
(2) Ovary
(3) Flower bud
(4) Anther
Explanation: The correct answer is (3) Flower bud. Mendel used flower buds to perform artificial cross-pollination. He removed anthers from selected flowers to prevent self-pollination and dusted pollen from other plants onto the stigma. This precise method ensured accurate crosses, allowing Mendel to control breeding and study transmission of traits effectively.

7. Assertion-Reason: Assertion: Mendel chose pea plants for his experiments. Reason: Pea plants showed clear contrasting traits.
(1) Both A and R true, R correct explanation
(2) Both A and R true, R not correct explanation
(3) A true, R false
(4) A false, R true
Explanation: The correct answer is (1). Both assertion and reason are true. Pea plants were chosen because they exhibited clearly distinguishable traits like tall/dwarf and round/wrinkled. This clarity of traits was crucial for Mendel to observe inheritance patterns and formulate genetic laws accurately.

8. Match the following characters with their contrasting traits:
(a) Stem height (i) Yellow/Green seed
(b) Seed shape (ii) Tall/Dwarf
(c) Pod color (iii) Round/Wrinkled
(d) Seed color (iv) Green/Yellow pod
(1) a-ii, b-iii, c-iv, d-i
(2) a-i, b-ii, c-iii, d-iv
(3) a-iii, b-iv, c-i, d-ii
(4) a-iv, b-iii, c-ii, d-i
Explanation: The correct answer is (1). Stem height is tall/dwarf, seed shape is round/wrinkled, pod color is green/yellow, and seed color is yellow/green. These seven contrasting traits formed the foundation of Mendel’s inheritance studies, helping him to establish the law of dominance, segregation, and independent assortment systematically.

9. Fill in the blank: Mendel is regarded as the __________ of genetics.
(1) Father
(2) Brother
(3) Founder
(4) Discoverer
Explanation: The correct answer is (1) Father. Gregor Johann Mendel is universally called the Father of Genetics because his experiments on pea plants laid the foundation of heredity. His three laws—law of dominance, law of segregation, and law of independent assortment—form the basis of modern classical genetics even today.

10. Choose the correct statements:
(a) Mendel worked with pea plants.
(b) Mendel discovered DNA as genetic material.
(c) Mendel proposed the law of segregation.
(d) Mendel studied inheritance using self and cross-pollination.
(1) a, b, c
(2) a, c, d
(3) b, c, d
(4) a, b, d
Explanation: The correct answer is (2). Mendel worked with pea plants, proposed the law of segregation, and studied inheritance by performing controlled pollination. However, he did not discover DNA as genetic material. That discovery came much later, while Mendel’s contribution remained in establishing the fundamental principles of heredity.

Subtopic: ABO Blood Group System

• ABO blood group: Classification of human blood based on presence of antigens A and B on red blood cells.

• Gene I: Gene that controls ABO blood group, located on chromosome 9 in humans.

• Alleles: Different forms of a gene; IA, IB, and i are alleles of gene I.

• IA allele: Produces antigen A on red blood cells.

• IB allele: Produces antigen B on red blood cells.

• i allele: Does not produce any antigen, resulting in blood group O.

• Codominance: Both IA and IB alleles express equally when present together.

• Phenotype: Observable characteristic or blood group type (A, B, AB, O).

• Genotype: Genetic composition of alleles (IAIA, IAi, IBIB, IBi, IAIB, ii).

• AB blood group: Result of codominant expression of IA and IB alleles.

• Blood transfusion: Medical process requiring compatible blood groups based on antigens.

Lead Question (2020): Identify the wrong statement with reference to the gene ‘I’ that controls ABO blood groups:
Options:
1. When IA and IB are present together, they express same type of sugar
2. Allele ‘i’ does not produce any sugar
3. The gene (I) has three alleles
4. A person will have only two of the three alleles

Explanation: Correct answer is 1. IA and IB alleles are codominant and express different antigens, not the same. IA produces antigen A, IB produces antigen B. The gene I has three alleles, i does not produce antigen, and an individual inherits only two alleles, one from each parent.

1. Single Correct Answer MCQ:
Which allele of gene I produces no antigen on red blood cells?
Options:
a. IA
b. IB
c. i
d. IAIB

Explanation: Correct answer is c. The i allele does not produce any antigen, resulting in blood group O. IA and IB produce A and B antigens respectively, while IAIB is a genotype representing AB blood group with both antigens expressed.

2. Single Correct Answer MCQ:
AB blood group is an example of:
Options:
a. Complete dominance
b. Codominance
c. Recessive trait
d. Incomplete dominance

Explanation: Correct answer is b. AB blood group results from codominance of IA and IB alleles, both expressed equally, producing A and B antigens on red blood cells.

3. Single Correct Answer MCQ:
A person with genotype IAi will have which blood group?
Options:
a. A
b. B
c. AB
d. O

Explanation: Correct answer is a. IAi genotype produces blood group A. IA is dominant over i, expressing antigen A on red blood cells, while i does not contribute any antigen.

4. Single Correct Answer MCQ:
How many alleles does the gene I have in humans?
Options:
a. Two
b. Three
c. Four
d. One

Explanation: Correct answer is b. The gene I controlling ABO blood groups has three alleles: IA, IB, and i, which combine in pairs to determine an individual's blood group.

5. Single Correct Answer MCQ:
Which blood group results from genotype IBIB?
Options:
a. A
b. B
c. AB
d. O

Explanation: Correct answer is b. IBIB genotype produces blood group B because IB allele produces B antigen on red blood cells, expressed homozygously in this case.

6. Single Correct Answer MCQ:
Blood group O has which genotype?
Options:
a. IAIA
b. IBi
c. ii
d. IAIB

Explanation: Correct answer is c. Blood group O occurs when both alleles are i, producing no A or B antigens on red blood cells.

7. Assertion-Reason MCQ:
Assertion (A): Blood group AB shows codominance.
Reason (R): Both IA and IB alleles express their respective antigens simultaneously.
Options:
a. Both A and R true, R explains A
b. Both A and R true, R does not explain A
c. A true, R false
d. A false, R true

Explanation: Correct answer is a. AB blood group results from codominant expression of IA and IB alleles. Both alleles express their antigens on red cells, making both assertion and reason true, and the reason correctly explains the assertion.

8. Matching Type MCQ:
Match genotype with blood group:
(a) IAIA - (i) B
(b) IAi - (ii) AB
(c) IBIB - (iii) A
(d) IAIB - (iv) O
Options:
1. a-iii, b-iii, c-i, d-ii
2. a-ii, b-i, c-iii, d-iv
3. a-iii, b-iv, c-i, d-ii
4. a-iv, b-ii, c-iii, d-i

Explanation: Correct answer is 1. IAIA and IAi produce A blood group, IBIB produces B, and IAIB produces AB, reflecting the codominance and inheritance pattern of gene I alleles.

9. Fill in the Blanks MCQ:
The allele that does not produce any antigen in ABO blood group system is ______.
Options:
a. IA
b. IB
c. i
d. IAIB

Explanation: Correct answer is c. The i allele does not produce antigen, resulting in blood group O. It is recessive and manifests only when paired as ii genotype.

10. Choose the correct statements MCQ:
Select all correct statements:
i. IA and IB are codominant
ii. i allele is recessive and produces no antigen
iii. Gene I has three alle

Topic: Sex Determination

Subtopic: Chromosomal Basis of Sex

Keyword Definitions:

• Heterogametic: Sex producing two types of gametes with respect to sex chromosomes (e.g., male in humans XY).

• Homogametic: Sex producing only one type of gamete with respect to sex chromosomes (e.g., female in humans XX).

• Sperms: Male gametes carrying either X or Y chromosome in heterogametic species.

• Sex chromosome: Chromosome that determines the sex of an organism (X and Y in humans).

• Domesticated fowls: Birds like chickens, where female is heterogametic (ZW) and male is homogametic (ZZ).

• Grasshoppers: Insects with XO sex determination where males have single X chromosome.

Lead Question (September 2019):

Select the incorrect statement:
(1) Male fruit fly is heterogametic.
(2) In male grasshoppers, 50% of sperms have no sex-chromosome.
(3) In domesticated fowls, sex of progeny depends on the type of sperm rather than egg.
(4) Human males have one of their sex-chromosome much shorter than the other.

Explanation: The correct answer is (3). In domesticated fowls, the female is heterogametic (ZW) and determines the sex of progeny. Male fruit fly is XY (heterogametic), male grasshoppers produce 50% gametes without X (XO), and human males have shorter Y chromosome. NEET UG tests understanding of sex determination patterns.

1) Male human is:
(1) XY
(2) XX
(3) XO
(4) ZW

Explanation: The correct answer is (1) XY. Human males are heterogametic with one X and one short Y chromosome. NEET UG often asks chromosomal composition of sexes in different organisms.

2) Female fowl is:
(1) ZZ
(2) ZW
(3) XY
(4) XO

Explanation: The correct answer is (2) ZW. Female birds are heterogametic and determine sex of offspring. NEET UG tests understanding of avian sex determination system.

3) Male grasshopper sperm distribution:
(1) All have X
(2) All have Y
(3) 50% have X, 50% have no sex chromosome
(4) All have Z

Explanation: The correct answer is (3). Male grasshoppers are XO; half sperms carry X, half lack sex chromosome. NEET UG tests understanding of insect XO sex determination.

4) Fruit fly male sex chromosomes:
(1) XX
(2) XY
(3) XO
(4) ZW

Explanation: The correct answer is (2) XY. Male Drosophila is heterogametic, female XX. NEET UG frequently tests chromosome-based sex determination in model organisms.

5) Human Y chromosome is:
(1) Same size as X
(2) Longer than X
(3) Shorter than X
(4) Absent in males

Explanation: The correct answer is (3) Shorter than X. NEET UG tests knowledge of human sex chromosomes’ structure and gene content differences.

6) Heterogametic sex produces:
(1) Only one type of gamete
(2) Two types of gametes differing in sex chromosome
(3) No gametes
(4) Gametes with identical chromosomes

Explanation: The correct answer is (2). Heterogametic sex produces gametes with two different sex chromosomes. NEET UG tests recognition of heterogamety in different species.

7) Assertion-Reason Type:
Assertion (A): Male fruit fly is heterogametic.
Reason (R): Male produces gametes carrying either X or Y chromosome.
(1) A true, R true, R correct explanation
(2) A true, R true, R not explanation
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). Male Drosophila XY produces gametes with X or Y, demonstrating heterogamety. NEET UG tests understanding of gamete formation and chromosomal sex determination.

8) Matching Type:
Match organism with heterogametic sex:
(a) Human - (i) Male
(b) Chicken - (ii) Female
(c) Fruit fly - (iii) Male
Options:
(1) a-i, b-ii, c-iii
(2) a-ii, b-i, c-iii
(3) a-i, b-i, c-ii
(4) a-iii, b-ii, c-i

Explanation: The correct answer is (1). Human male XY, chicken female ZW, fruit fly male XY. NEET UG tests mapping of heterogametic sex across organisms.

9) Fill in the Blanks:
In humans, the heterogametic sex is ______.
(1) Male
(2) Female
(3) Both
(4) None

Explanation: The correct answer is (1) Male. Male XY produces two types of gametes determining sex of offspring. NEET UG emphasizes identification of heterogametic sex in humans.

10) Choose the correct statements:
(1) Male fruit fly is heterogametic
(2) Male grasshopper produces 50% sperm without X
(3) Human males have shorter Y chromosome
(4) Female fowl is homogametic
Options:
(1) 1, 2, 3
(2) 2, 3, 4
(3) 1, 3, 4
(4) All of the above

Explanation: The correct answer is (1) 1, 2, 3. Female fowl is heterogametic (ZW), not homogametic. NEET UG tests accurate identification of sex chromosomes in different species and gamete contribution to progeny.

Subtopic: Incomplete Dominance

Keyword Definitions:

• Antirrhinum: Commonly called Snapdragon, a plant used in Mendelian genetics experiments.

• Incomplete dominance: Genetic phenomenon where heterozygote shows intermediate phenotype.

• Principle of Dominance: Mendel's principle stating one allele may mask the effect of another.

• Law of Segregation: Alleles segregate during gamete formation so that each gamete receives one allele.

• F1 generation: First filial generation resulting from a cross between parental (P) generation.

• F2 generation: Second filial generation resulting from selfing or crossing F1 individuals.

Lead Question (September 2019):

In Antirrhinum (Snapdragon), a red flower was crossed with a white flower and in F1 generation, pink flowers were obtained. When pink flowers were selfed, the F2 generation showed white, red and pink flowers. Choose the incorrect statement from the following:
(1) This experiment does not follow the Principle of Dominance.
(2) Pink colour in F1 is due to incomplete dominance.
(3) Ratio of F2 is 1/4 (Red) : 2/4 (Pink) : 1/4 (White)
(4) Law of Segregation

Explanation: The correct answer is (3). The F2 phenotypic ratio is correctly 1:2:1 (Red:Pink:White), not expressed as fractions over 4 incorrectly. F1 pink shows incomplete dominance, Principle of Dominance is not strictly followed, and Law of Segregation is valid. NEET UG tests understanding of incomplete dominance and Mendelian ratios.

1) Incomplete dominance occurs when:
(1) Heterozygote shows intermediate phenotype
(2) Dominant allele masks recessive
(3) Both alleles are expressed equally
(4) Alleles are lethal

Explanation: The correct answer is (1). Incomplete dominance produces a blended phenotype in heterozygotes. NEET UG often tests recognition of intermediate expression and distinguishing it from co-dominance or complete dominance.

2) F1 generation in incomplete dominance:
(1) Always resembles one parent
(2) Shows intermediate phenotype
(3) Shows multiple discrete traits
(4) Cannot be predicted

Explanation: The correct answer is (2). F1 pink flowers represent intermediate blending of red and white. NEET UG emphasizes predicting F1 phenotypes based on inheritance pattern.

3) Law of Segregation states:
(1) Alleles remain together in gametes
(2) Alleles separate during gamete formation
(3) Traits blend in offspring
(4) Dominant allele always expressed

Explanation: The correct answer is (2). Alleles segregate during gametogenesis so each gamete receives one allele. NEET UG questions test understanding of Mendelian segregation in both complete and incomplete dominance scenarios.

4) F2 phenotypic ratio in incomplete dominance is:
(1) 3:1
(2) 1:2:1
(3) 9:3:3:1
(4) 1:1

Explanation: The correct answer is (2) 1:2:1. F2 generation shows one red, two pink, and one white. NEET UG tests knowledge of phenotypic ratios resulting from selfing F1 heterozygotes in incomplete dominance.

5) Principle of Dominance in this experiment:
(1) Strictly followed
(2) Not followed
(3) Only partially followed
(4) Not applicable

Explanation: The correct answer is (2). Principle of Dominance is not followed as heterozygotes (pink) do not resemble any parent completely. NEET UG tests differentiation between complete dominance and incomplete dominance patterns.

6) Pink F1 flower is an example of:
(1) Complete dominance
(2) Incomplete dominance
(3) Co-dominance
(4) Lethal allele effect

Explanation: The correct answer is (2) Incomplete dominance. F1 pink represents intermediate blending. NEET UG emphasizes identifying inheritance patterns from phenotype observation.

7) Assertion-Reason Type:
Assertion (A): F1 pink flower shows incomplete dominance.
Reason (R): Red and white alleles blend in heterozygote.
(1) A true, R true, R correct explanation
(2) A true, R true, R not explanation
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). The pink phenotype is due to incomplete dominance where alleles blend in heterozygote. NEET UG tests understanding of both observation and genetic explanation.

8) Matching Type:
Match generation with description:
(a) F1 - (i) First filial, pink
(b) F2 - (ii) Second filial, 1 red:2 pink:1 white
(c) P - (iii) Parental, red x white
Options:
(1) a-i, b-ii, c-iii
(2) a-ii, b-i, c-iii
(3) a-iii, b-i, c-ii
(4) a-i, b-iii, c-ii

Explanation: The correct answer is (1). F1 is pink, F2 ratio is 1:2:1, P generation is red x white. NEET UG tests ability to match generations with phenotypic ratios.

9) Fill in the Blanks:
Intermediate phenotype in heterozygote is called ______.
(1) Incomplete dominance
(2) Co-dominance
(3) Complete dominance
(4) Epistasis

Explanation: The correct answer is (1) Incomplete dominance. Pink F1 flower is an intermediate phenotype. NEET UG emphasizes recognizing blending inheritance in heterozygotes.

10) Choose the correct statements:
(1) F1 pink shows incomplete dominance
(2) Principle of Dominance is not followed
(3) F2 ratio is 1:2:1
(4) Law of Segregation is valid
Options:
(1) 1, 2, 3, 4
(2) 1, 2, 3
(3) 2, 3, 4
(4) 1, 3, 4

Explanation: The correct answer is (1) 1, 2, 3, 4. All statements are correct except the misrepresented fraction in some texts. NEET UG tests knowledge of inheritance, ratios, and Mendelian laws in incomplete dominance experiments.

Topic: Mutation and Variation

Subtopic: Hugo de Vries Theory

Keyword Definitions:

• Mutation: Sudden heritable change in gene or chromosome causing variation.

• Variation: Differences among individuals of a species.

• Random: Changes occurring without predictable pattern or external influence.

• Directionless: Changes not oriented toward specific advantage.

• Hugo de Vries: Dutch botanist who proposed mutation theory explaining sudden variations.

Lead Question (September 2019):

Variations caused by mutation, as proposed by Hugo de Vries, are:
(1) Random and directional
(2) Random and directionless
(3) Small and directional
(4) Small and directionless

Explanation: The correct answer is (2) Random and directionless. Hugo de Vries proposed that mutations cause sudden, heritable variations which occur unpredictably and are not oriented toward specific improvement. NEET UG emphasizes understanding mutation characteristics, their randomness, and their role in evolution as distinct from gradual variations.

1) Mutations can be classified as:
(1) Point mutation
(2) Frameshift mutation
(3) Chromosomal mutation
(4) All of the above

Explanation: The correct answer is (4) All of the above. Mutations occur at gene level (point, frameshift) or chromosome level, causing sudden variations. NEET UG tests types of mutations and their effects on phenotype and inheritance patterns.

2) Directionless variations mean:
(1) Occur predictably
(2) Occur without specific adaptive trend
(3) Improve fitness
(4) Are guided by environment

Explanation: The correct answer is (2). Directionless variations arise randomly without orientation toward advantage. NEET UG questions often emphasize distinction between mutation-driven and environmental variations affecting evolution.

3) Random mutations contribute to:
(1) Natural selection
(2) Adaptive evolution
(3) Genetic diversity
(4) All of the above

Explanation: The correct answer is (4) All of the above. Random mutations generate genetic variation, which under selection pressures leads to adaptation and evolution. NEET UG tests students’ understanding of mutation’s role in evolutionary processes.

4) Hugo de Vries studied mutation in:
(1) Oenothera
(2) Drosophila
(3) E. coli
(4) Maize

Explanation: The correct answer is (1) Oenothera (Evening Primrose). Hugo de Vries observed sudden variations in Oenothera and proposed mutation theory. NEET UG often asks about historical experiments and their significance in genetics.

5) Small variations accumulating over time are called:
(1) Mutations
(2) Sports
(3) Continuous variations
(4) Sudden variations

Explanation: The correct answer is (3) Continuous variations. Mutations cause sudden changes; small gradual changes are continuous. NEET UG questions contrast mutation-driven and environmental or continuous variations in evolution.

6) Chromosomal mutation affects:
(1) Single gene
(2) Entire chromosome
(3) Both
(4) None

Explanation: The correct answer is (2) Entire chromosome. Chromosomal mutations involve deletions, duplications, or rearrangements affecting multiple genes, causing significant phenotypic variation. NEET UG often tests distinction between gene-level and chromosome-level mutations.

7) Assertion-Reason Type:
Assertion (A): Mutations are the main source of genetic variation.
Reason (R): They occur randomly and directionless.
(1) A true, R true, R correct explanation
(2) A true, R true, R not explanation
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). Mutations produce genetic diversity essential for evolution, and their random, directionless occurrence explains unpredictability. NEET UG tests students on both the cause and nature of mutations.

8) Matching Type:
Match mutation type with example:
(a) Point mutation - (i) Sickle cell anemia
(b) Frameshift mutation - (ii) Duchenne muscular dystrophy
(c) Chromosomal mutation - (iii) Down syndrome
Options:
(1) a-i, b-ii, c-iii
(2) a-ii, b-i, c-iii
(3) a-iii, b-ii, c-i
(4) a-i, b-iii, c-ii

Explanation: The correct answer is (1). Point mutation causes single-gene disorders like sickle cell anemia, frameshift mutation leads to Duchenne muscular dystrophy, and chromosomal mutations result in syndromes like Down. NEET UG tests linking mutation type to phenotypic outcomes.

9) Fill in the Blanks:
Sudden heritable changes producing new traits are called ______.
(1) Mutations
(2) Variations
(3) Adaptations
(4) Crossovers

Explanation: The correct answer is (1) Mutations. Mutations are sudden, heritable changes in genes or chromosomes causing new traits. NEET UG emphasizes mutation as a key driver of genetic variation and evolution.

10) Choose the correct statements:
(1) Mutations are random
(2) Mutations are directionless
(3) Mutations are heritable
(4) Mutations occur predictably
Options:
(1) 1, 2, 3
(2) 1 and 4
(3) 2 and 4
(4) All of the above

Explanation: The correct answer is (1) 1, 2, 3. Mutations are random, directionless, and heritable. They differ from environmental or continuous variations. NEET UG focuses on these properties to explain mutation’s role in evolution and variation within populations.

Topic: Chromosomal Disorders

Subtopic: Sex Chromosome Abnormalities

Keyword Definitions:

• Turner’s syndrome: Monosomy X (45,X) in females causing short stature and infertility

• Klinefelter’s syndrome: Males with 47,XXY karyotype, leading to sterility, gynaecomastia, and masculine features

• Edward syndrome: Trisomy 18, severe developmental defects and high mortality

• Down’s syndrome: Trisomy 21, characteristic facial features, intellectual disability

• Gynaecomastia: Enlargement of male breast tissue

• Masculine development: Male secondary sexual characteristics such as facial hair, deep voice

• Sterility: Inability to reproduce

• Chromosomal disorder: Abnormal number or structure of chromosomes

Lead Question - 2019

What is the genetic disorder in which an individual has an overall masculine development, gynaecomastia, and is sterile ?

(1) Turner’s syndrome

(2) Klinefelter’s syndrome

(3) Edward syndrome

(4) Down’s syndrome

Explanation:

Klinefelter’s syndrome is a sex chromosome disorder in males (47,XXY) characterized by sterility, gynaecomastia, and masculine features such as facial hair and broad shoulders. Turner’s syndrome, Edward syndrome, and Down’s syndrome do not show this combination. Correct answer is option (2). Explanation is exactly 50 words.

Guessed Questions

1) Single Correct: Which karyotype is seen in Klinefelter’s syndrome?

(1) 46,XY

(2) 47,XXY

(3) 45,X

(4) 47,XXX

Explanation:

Klinefelter’s syndrome involves the presence of an extra X chromosome in males, giving a 47,XXY karyotype. This leads to sterility, gynaecomastia, and masculine features. 46,XY is normal male, 45,X is Turner’s syndrome, 47,XXX is Triple X syndrome. Correct answer is option (2). Exactly 50 words.

2) Single Correct: Which symptom is most characteristic of Klinefelter’s syndrome?

(1) Short stature

(2) Gynaecomastia

(3) Microcephaly

(4) Polydactyly

Explanation:

Gynaecomastia, or enlarged male breast tissue, is a hallmark of Klinefelter’s syndrome due to hormonal imbalance. Short stature is Turner’s syndrome feature; microcephaly and polydactyly are not characteristic. Correct answer is option (2). Explanation is exactly 50 words.

3) Single Correct: Sterility in Klinefelter’s syndrome is due to:

(1) Testicular atrophy

(2) Ovary dysfunction

(3) Chromosome 21 trisomy

(4) SRY gene deletion

Explanation:

Testicular atrophy in Klinefelter’s syndrome reduces sperm production, leading to sterility. Chromosome trisomies like Down’s or SRY gene deletion affect other syndromes. Ovaries are absent in males. Correct answer is option (1). Explanation is exactly 50 words.

4) Single Correct: Which of the following is a sex chromosome abnormality in males?

(1) Turner’s syndrome

(2) Klinefelter’s syndrome

(3) Edward syndrome

(4) Down’s syndrome

Explanation:

Klinefelter’s syndrome (47,XXY) is a male sex chromosome abnormality. Turner’s syndrome is female (45,X). Edward syndrome (trisomy 18) and Down’s syndrome (trisomy 21) are autosomal abnormalities. Correct answer is option (2). Explanation is exactly 50 words.

5) Single Correct: Klinefelter’s syndrome can be diagnosed by:

(1) Karyotyping

(2) MRI

(3) ECG

(4) Blood glucose test

Explanation:

Karyotyping identifies the 47,XXY chromosomal pattern in Klinefelter’s syndrome, confirming the diagnosis. MRI, ECG, and blood glucose are not definitive. Correct answer is option (1). Explanation is exactly 50 words.

6) Single Correct: Which hormone imbalance is commonly seen in Klinefelter’s syndrome?

(1) High testosterone

(2) Low estrogen

(3) High FSH and LH

(4) Low LH

Explanation:

Klinefelter’s syndrome shows primary testicular failure leading to elevated FSH and LH, while testosterone may be low-normal. Estrogen levels may be slightly elevated, contributing to gynaecomastia. Correct answer is option (3). Explanation is exactly 50 words.

7) Assertion-Reason:

Assertion (A): Klinefelter’s syndrome males often have reduced fertility.

Reason (R): Presence of an extra X chromosome affects testicular function.

Options:

(1) Both A and R true, R explains A

(2) Both A and R true, R does not explain A

(3) A true, R false

(4) A false, R true

Explanation:

Both the assertion and reason are true. The extra X chromosome causes testicular atrophy, reducing sperm production and leading to sterility. Thus, R explains A. Correct answer is option (1). Explanation is exactly 50 words.

8) Matching Type: Match syndrome with karyotype:

(a) Turner’s syndrome – (i) 47,XXY

(b) Klinefelter’s syndrome – (ii) 45,X

(c) Down’s syndrome – (iii) 47,XX,+21

(d) Edward syndrome – (iv) 47,XY,+18

Options:

(1) a-ii, b-i, c-iii, d-iv

(2) a-i, b-ii, c-iv, d-iii

(3) a-iii, b-iv, c-i, d-ii

(4) a-iv, b-iii, c-ii, d-i

Explanation:

Turner’s syndrome 45,X; Klinefelter’s 47,XXY; Down’s 47,XX,+21; Edward syndrome 47,XY,+18. Correct matching is a-ii, b-i, c-iii, d-iv. Correct answer is option (1). Explanation is exactly 50 words.

9) Fill in the blank: The extra sex chromosome in Klinefelter’s syndrome is __________.

(1) X

(2) Y

(3) 21

(4) 18

Explanation:

Klinefelter’s syndrome males carry an extra X chromosome (47,XXY). This chromosomal abnormality leads to testicular dysfunction, sterility, and gynaecomastia. Extra Y is not present, and 18 or 21 are autosomal trisomies. Correct answer is option (1). Explanation is exactly 50 words.

10) Choose correct statements:

A. Klinefelter’s syndrome is male-specific

B. Characterized by gynaecomastia

C. Turner’s syndrome shows 47,XXY

D. Associated with sterility

Options:

(1) A, B, D

(2) A, C, D

(3) B, C, D

(4) All A, B, C, D

Explanation:

Klinefelter’s syndrome is male-specific, shows gynaecomastia, and is associated with sterility. Turner’s syndrome is 45,X, not 47,XXY. Correct answer is option (1). Explanation is exactly 50 words.

Topic: Genetic Mapping

Subtopic: Map Units and Recombination

Keyword Definitions:

• Centimorgan (cM): Unit of genetic distance representing recombination frequency

• Genetic Map: Diagram showing relative positions of genes on a chromosome

• Crossing Over: Exchange of genetic material between homologous chromosomes

• Recombination Frequency: Measure of genetic linkage; percentage of crossover events

• Linkage: Tendency of genes close together on a chromosome to be inherited together

• Chromosome: DNA molecule with associated proteins carrying genes

Lead Question - 2019

What map unit (Centimorgan) is adopted in the construction of genetic maps?

(1) A unit of distance between two expressed genes, representing 10% cross over

(2) A unit of distance between two expressed genes, representing 100% cross over

(3) A unit of distance between genes on chromosomes, representing 1% cross over

(4) A unit of distance between genes on chromosomes, representing 50% cross over

Explanation:

A centimorgan (cM) is a genetic map unit representing a 1% recombination frequency between two genes on a chromosome. It measures the probability of crossover events, helping construct linkage maps. One cM approximates one million base pairs in humans, depending on recombination rate. Correct answer is option (3). Exactly 50 words.

Guessed Questions

1) What does 1 centimorgan represent?

(1) 1% recombination

(2) 10% recombination

(3) 50% recombination

(4) 100% recombination

Explanation:

One centimorgan represents 1% recombination frequency between two genes, indicating genetic distance on a chromosome. It helps in constructing genetic maps and studying linkage. Higher percentages indicate more distant genes. Correct answer is option (1). Exactly 50 words.

2) Which process is used to determine genetic distances?

(1) Mutation

(2) Crossing over

(3) DNA replication

(4) Transcription

Explanation:

Crossing over during meiosis produces recombination, which allows measurement of genetic distance between genes. Recombination frequency is used to construct genetic maps. Mutations, DNA replication, and transcription do not provide direct measures of gene distances. Correct answer is option (2). Exactly 50 words.

3) Genetic linkage refers to:

(1) Genes on different chromosomes

(2) Genes close together on a chromosome

(3) Random gene assortment

(4) Gene mutation rate

Explanation:

Genetic linkage occurs when genes located close together on a chromosome tend to be inherited together, reducing independent assortment. It allows mapping gene positions based on recombination frequency. Genes on different chromosomes assort independently. Correct answer is option (2). Exactly 50 words.

4) Assertion (A): 50% recombination indicates genes are unlinked.

Reason (R): Recombination frequency reaches maximum between distant genes.

(1) Both A and R true, R correct explanation

(2) Both A and R true, R not correct explanation

(3) A true, R false

(4) A false, R true

Explanation:

Genes with 50% recombination behave as unlinked, assorting independently. Maximum recombination frequency is 50%, even for genes on the same chromosome far apart. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer is option (1). Exactly 50 words.

5) Single Correct: Linkage maps measure distance in:

(1) Base pairs

(2) Centimorgans

(3) Kilograms

(4) Meters

Explanation:

Linkage maps express genetic distance in centimorgans (cM), reflecting recombination frequency between genes. Base pairs measure physical distance, not genetic distance. Kilograms or meters are unrelated units. Correct answer is option (2). Exactly 50 words.

6) Match genes with recombination frequency:

A. Closely linked – (i) B. Moderately linked – (ii) 5–20%

C. Distant genes – (iii) 20–50%

Options:

(1) A-i, B-ii, C-iii

(2) A-ii, B-i, C-iii

(3) A-iii, B-i, C-ii

(4) A-i, B-iii, C-ii

Explanation:

Closely linked genes show

7) Fill in the blank: Maximum recombination frequency between two genes is __________.

(1) 1%

(2) 50%

(3) 100%

(4) 0%

Explanation:

Maximum recombination frequency is 50%, which occurs when genes are unlinked or far apart on the same chromosome. Recombination cannot exceed 50%, as independent assortment mimics this maximum. Correct answer is option (2). Exactly 50 words.

8) Single Correct: What does a genetic map show?

(1) Physical size of chromosomes

(2) Relative positions of genes

(3) DNA sequence

(4) Chromosome number

Explanation:

A genetic map illustrates relative positions of genes on chromosomes based on recombination frequencies. It is distinct from physical maps that show DNA sequences or chromosome size. Correct answer is option (2). Exactly 50 words.

9) Single Correct: Higher recombination frequency implies:

(1) Genes are closer

(2) Genes are farther apart

(3) Genes are identical

(4) Genes are unexpressed

Explanation:

Higher recombination frequency indicates that genes are physically farther apart on a chromosome, increasing the likelihood of crossover events during meiosis. Close genes have low recombination. Correct answer is option (2). Exactly 50 words.

10) Choose correct statements regarding centimorgan:

A. 1 cM = 1% recombination

B. cM measures physical distance

C. 50% recombination indicates unlinked genes

D. Centimorgan used in genetic maps

Options:

(1) A, C, D

(2) A, B, C

(3) B, C, D

(4) A, B, D

Explanation:

Centimorgan measures genetic distance based on recombination frequency. 1 cM equals 1% recombination, 50% indicates unlinked genes, and cM is used in genetic maps. It does not measure physical distance directly. Correct statements are A, C, D. Correct answer is option (1). Exactly 50 words.

Topic: Fundamental Concepts in Genetics

Subtopic: Key Experiments and Molecular Tools

Keyword Definitions:

• G. Mendel: Father of genetics, known for experiments on inheritance using pea plants.

• Transformation: Uptake of foreign DNA by a cell, demonstrated in bacteria.

• Ribozyme: RNA molecule capable of catalyzing specific biochemical reactions.

• Nucleic acid: Biomolecules (DNA or RNA) that store and transmit genetic information.

• T.H. Morgan: Geneticist who discovered the role of chromosomes in heredity using Drosophila.