Cell Division

Subtopic: Meiosis

Keyword Definitions:

• Meiosis: Type of cell division producing gametes with half the chromosome number.

• Prophase-I: First stage of Meiosis-I, where chromosomes condense, pair, and recombine.

• Chromosome compaction: Condensation of chromatin into visible chromosomes.

• Synaptonemal complex: Protein structure facilitating pairing of homologous chromosomes.

• Crossing over: Exchange of genetic material between non-sister chromatids.

• Chiasmata: Points of crossover visible under a microscope.

• Terminalisation: Movement of chiasmata towards chromosome ends.

• Nuclear envelope breakdown: Disassembly of nuclear membrane to allow spindle access.

• Homologous chromosomes: Chromosome pairs containing same genes from each parent.

• Gametes: Haploid reproductive cells produced by meiosis.

• Genetic recombination: Rearrangement of genetic material during meiosis leading to diversity.

Lead Question - 2022 (Abroad)

Select the correct sequence of events occurring during Prophase-I of Meiosis-I

1. Nuclear envelope breakdown

2. Synaptonemal complex formation

3. Compaction of chromosomes

4. Terminalisation of chiasmata

5. Crossing over

Explanation: The sequence during Prophase-I begins with chromosome compaction to make them visible, followed by formation of the synaptonemal complex, then crossing over occurs at chiasmata, which later terminalise. Finally, nuclear envelope breakdown occurs to allow spindle attachment. This precise order ensures proper recombination and segregation of homologous chromosomes. Correct answer: 1

1. SINGLE CORRECT ANSWER MCQ

During which sub-stage of Prophase-I does crossing over occur?

1. Leptotene

2. Zygotene

3. Pachytene

4. Diplotene

Explanation: Crossing over occurs during the pachytene stage of Prophase-I, after homologous chromosomes synapse via the synaptonemal complex. This allows exchange of genetic material, increasing genetic diversity. Leptotene involves condensation, zygotene pairing, and diplotene shows chiasmata becoming visible. Correct answer: 3

2. SINGLE CORRECT ANSWER MCQ

Which protein structure stabilizes homologous chromosome pairing?

1. Spindle fibers

2. Synaptonemal complex

3. Centromere

4. Kinetochore

Explanation: The synaptonemal complex is a protein scaffold that holds homologous chromosomes together during zygotene and pachytene. This stabilizes pairing and facilitates crossing over. Spindle fibers attach later to kinetochores; centromeres are central chromosome regions, not pairing structures. Correct answer: 2

3. SINGLE CORRECT ANSWER MCQ

Terminalisation refers to:

1. Chromosome condensation

2. Movement of chiasmata toward chromosome ends

3. Breakdown of nuclear envelope

4. Alignment at metaphase plate

Explanation: Terminalisation is the process in diplotene where chiasmata move towards the ends of homologous chromosomes, facilitating proper segregation during anaphase-I. Condensation, nuclear envelope breakdown, and metaphase alignment occur at other stages. Correct answer: 2

4. SINGLE CORRECT ANSWER MCQ

Which event directly follows chromosome compaction in Prophase-I?

1. Synaptonemal complex formation

2. Crossing over

3. Nuclear envelope breakdown

4. Terminalisation

Explanation: After chromosomes condense, homologous chromosomes pair via synaptonemal complex formation. This pairing is essential for subsequent crossing over. Nuclear envelope breakdown and terminalisation occur later to allow spindle attachment and chromosome segregation. Correct answer: 1

5. SINGLE CORRECT ANSWER MCQ

Leptotene stage is characterized by:

1. Chromosome condensation

2. Chiasmata formation

3. Synapsis completion

4. Nuclear envelope breakdown

Explanation: Leptotene is the first sub-stage of Prophase-I where chromosomes condense into visible threads. Synapsis and chiasmata formation occur later in zygotene and pachytene. Nuclear envelope breakdown occurs at late prophase-I. Correct answer: 1

6. SINGLE CORRECT ANSWER MCQ

Which stage allows homologous recombination to increase genetic diversity?

1. Pachytene

2. Diplotene

3. Leptotene

4. Metaphase-I

Explanation: Genetic recombination occurs during pachytene through crossing over. This exchange of genetic material between homologous chromatids increases diversity. Diplotene and leptotene involve condensation and chiasmata visualization, while metaphase-I is alignment for segregation. Correct answer: 1

7. ASSERTION-REASON MCQ

Assertion (A): Crossing over occurs during pachytene stage.

Reason (R): Synaptonemal complex brings homologous chromosomes together for recombination.

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 but R is false

4. A is false but R is true

Explanation: Crossing over occurs during pachytene, facilitated by the synaptonemal complex which aligns homologous chromosomes precisely. Both assertion and reason are correct, and the reason explains the occurrence of crossing over. Correct answer: 1

8. MATCHING TYPE MCQ

Match Prophase-I sub-stages with their key event:

Column A:

1. Leptotene

2. Zygotene

3. Pachytene

4. Diplotene

5. Diakinesis

Column B:

1. Chromosome condensation begins

2. Synapsis starts

3. Crossing over occurs

4. Chiasmata visible

5. Terminalisation and nuclear envelope breakdown

Explanation: Leptotene → condensation, Zygotene → synapsis, Pachytene → crossing over, Diplotene → chiasmata visible, Diakinesis → terminalisation and nuclear envelope breakdown. These sequential events ensure genetic recombination and proper chromosome segregation. Correct answer: 1-A, 2-B, 3-C, 4-D, 5-E

9. FILL IN THE BLANKS / COMPLETION MCQ

The structure that facilitates pairing of homologous chromosomes during Prophase-I is called ________.

1. Spindle fiber

2. Synaptonemal complex

3. Centromere

4. Chiasma

Explanation: The synaptonemal complex is a proteinaceous structure connecting homologous chromosomes during zygotene and pachytene. It stabilizes pairing, ensures crossing over, and maintains alignment until separation. Spindle fibers and centromeres have different roles, and chiasma is a site of crossover. Correct answer: 2

10. CHOOSE THE CORRECT STATEMENTS MCQ

Statement I: Terminalisation occurs in diakinesis.
Statement II: Pachytene is when homologous chromosomes separate completely.

1. Only Statement I is correct

2. Only Statement II is correct

3. Both Statements I and II are correct

4. Both Statements I and II are incorrect

Explanation: Terminalisation and nuclear envelope breakdown occur in diakinesis preparing for metaphase-I. Pachytene involves synapsis and crossing over, not separation. Hence only Statement I is correct. Correct answer: 1

Topic: Oogenesis; Subtopic: Arrested Stages of Oocytes

Keyword Definitions:

• Oocyte: Female gamete involved in sexual reproduction, developing into an ovum.

• Arrested stage: Phase of meiosis in which oocytes remain suspended for prolonged periods.

• Diplotene: Substage of prophase I where homologous chromosomes begin to separate but remain connected at chiasmata.

• Telophase-I: Final stage of first meiotic division, chromosomes arrive at poles and cytoplasm divides.

• Diakinesis: Last substage of prophase I, characterized by chromosome condensation and nuclear envelope breakdown.

• Metaphase-I: Stage of meiosis I where homologous chromosome pairs align at the equatorial plane.

• Vertebrates: Animals with a backbone or spinal column.

• Meiosis: Type of cell division producing haploid gametes with genetic variation.

• Gametogenesis: Process of formation of gametes, including oogenesis and spermatogenesis.

• Chiasmata: Points where homologous chromosomes exchange genetic material during crossing-over.

• Ovulation: Release of mature ovum from the ovary into the oviduct.

Lead Question - 2022 (Abroad)

The oocytes of some vertebrates get arrested for years or months in:

1. Telophase-I

2. Diplotene

3. Diakinesis

4. Metaphase-I

Explanation: In many vertebrates, primary oocytes pause in diplotene of prophase I for months or even years until hormonal signals resume meiosis during ovulation. This arrest allows time for growth, accumulation of nutrients, and maintenance of genetic integrity. Telophase-I, diakinesis, and metaphase-I occur later in meiosis and are not stages where oocytes remain suspended long-term. This arrested stage is crucial for coordinating reproductive timing with organismal maturity. Correct answer: 2

1. SINGLE CORRECT ANSWER MCQ

Which stage of meiosis is completed just before ovulation in vertebrates?

1. Prophase-I

2. Metaphase-II

3. Diplotene

4. Telophase-II

Explanation: In vertebrates, the primary oocyte resumes meiosis during ovulation and completes meiosis I. The secondary oocyte then arrests at metaphase-II until fertilization occurs. Prophase-I and diplotene are arrested earlier, while telophase-II occurs only after fertilization. This mechanism ensures the oocyte is ready for fertilization at the correct developmental stage. Correct answer: 2

2. SINGLE CORRECT ANSWER MCQ

Chiasmata are visible during which substage of oocyte meiosis?

1. Diplotene

2. Metaphase-I

3. Telophase-I

4. Diakinesis

Explanation: Chiasmata, the sites of genetic recombination, become visible in the diplotene stage of prophase I. They maintain homologous chromosome association while allowing crossing-over. This stage also corresponds to the long arrest period in vertebrate oocytes. Metaphase-I, telophase-I, and diakinesis occur later and do not display chiasmata prominently. Correct answer: 1

3. SINGLE CORRECT ANSWER MCQ

The arrested oocyte in diplotene is referred to as:

1. Secondary oocyte

2. Primary oocyte

3. Polar body

4. Ovum

Explanation: Primary oocytes in vertebrates are arrested at diplotene of prophase I and remain so until hormonal cues trigger ovulation. The secondary oocyte forms after completion of meiosis I. Polar bodies are byproducts of unequal cytokinesis, and ovum refers to the mature female gamete. Arrest at diplotene ensures oocyte readiness and genomic stability. Correct answer: 2

4. SINGLE CORRECT ANSWER MCQ

Which hormone triggers resumption of meiosis in the arrested oocyte?

1. FSH

2. LH

3. Progesterone

4. Prolactin

Explanation: Luteinizing hormone (LH) surge induces the resumption of meiosis in arrested primary oocytes. This triggers completion of meiosis I and formation of a secondary oocyte at metaphase-II, preparing it for ovulation. FSH promotes follicle development, progesterone maintains the uterine lining, and prolactin supports lactation. Correct answer: 2

5. SINGLE CORRECT ANSWER MCQ

During which stage is the nuclear envelope broken down before meiotic division?

1. Diakinesis

2. Diplotene

3. Telophase-I

4. Metaphase-I

Explanation: Diakinesis is the final stage of prophase I where chromosomes condense fully and the nuclear envelope breaks down, preparing the oocyte for metaphase-I alignment. Diplotene involves chiasmata and prolonged arrest, telophase-I occurs after chromosome separation, and metaphase-I is alignment at the equator. Correct answer: 1

6. SINGLE CORRECT ANSWER MCQ

Which statement about vertebrate oocyte arrest is correct?

1. Oocytes arrest in metaphase-II for years

2. Oocytes arrest in diplotene of prophase-I

3. Oocytes do not undergo arrest

4. Oocytes arrest in telophase-II permanently

Explanation: Vertebrate oocytes are arrested in diplotene of prophase I for months or years until hormonal signals resume meiosis. Metaphase-II arrest occurs temporarily until fertilization, while telophase-II and continuous progression without arrest do not occur naturally. Diplotene arrest ensures adequate growth, maturation, and genomic integrity of the oocyte. Correct answer: 2

7. ASSERTION-REASON MCQ

Assertion (A): Primary oocytes remain arrested at diplotene for years in many vertebrates.

Reason (R): Arrest allows time for oocyte growth, nutrient accumulation, and genomic maintenance before ovulation.

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 but R is false

4. A is false but R is true

Explanation: Primary oocytes in vertebrates remain arrested at diplotene of prophase-I to accumulate cytoplasmic nutrients, maintain genomic integrity, and await hormonal signals for ovulation. Both the assertion and reason are true, and the reason explains the purpose of the arrest, ensuring reproductive success. Correct answer: 1

8. MATCHING TYPE MCQ

Match the stage of meiosis with its description:

Column A:

1. Diplotene

2. Diakinesis

3. Metaphase-I

4. Telophase-I

Column B:

1. Chromosomes condense and nuclear envelope breaks down

2. Long arrest of primary oocytes

3. Chromosomes align at equatorial plane

4. Chromosomes reach poles and cytoplasm divides

Explanation: Correct matching: Diplotene → Long arrest of primary oocytes, Diakinesis → Chromosomes condense and nuclear envelope breaks down, Metaphase-I → Chromosomes align at equator, Telophase-I → Chromosomes reach poles and cytoplasm divides. These stages sequentially regulate meiosis and prepare oocytes for fertilization. Correct answer: 1-B, 2-A, 3-C, 4-D

9. FILL IN THE BLANKS / COMPLETION MCQ

Primary oocytes in vertebrates remain arrested in ________ until hormonal signals trigger ovulation.

1. Telophase-I

2. Diplotene

3. Metaphase-II

4. Diakinesis

Explanation: Primary oocytes are arrested in the diplotene stage of prophase-I for extended periods in vertebrates. This allows time for oocyte growth, nutrient accumulation, and maintenance of genomic integrity. Hormonal signals resume meiosis leading to secondary oocyte formation. Other stages occur later or only briefly. Correct answer: 2

10. CHOOSE THE CORRECT STATEMENTS MCQ

Statement I: Diplotene stage arrest is essential for oocyte maturation.
Statement II: Telophase-I arrest is common in vertebrate oocytes.

1. Only Statement I is correct

2. Only Statement II is correct

3. Both Statements I and II are correct

4. Both Statements I and II are incorrect

Explanation: The arrest at diplotene allows oocytes to grow, accumulate nutrients, and maintain genetic stability. Telophase-I arrest does not occur; meiosis progresses normally to metaphase-II after resumption. Therefore, only Statement I is correct. Correct answer: 1

Topic: Meiosis; Subtopic: Prophase I and Diplotene Stage

• Diplotene: A sub-stage of prophase I of meiosis where homologous chromosomes begin to separate but remain attached at chiasmata.

• Synaptonemal Complex: Protein structure that forms between homologous chromosomes during meiosis, facilitating pairing and recombination.

• Chiasmata: X-shaped regions where crossing over occurs between homologous chromosomes.

• Oocyte: Female gamete or egg cell undergoing meiosis.

• Meiosis: Type of cell division that reduces chromosome number by half to form gametes.

• Prophase I: First stage of meiosis I during which chromosomes condense and homologous chromosomes pair.

• Crossing over: Exchange of genetic material between homologous chromosomes at chiasmata.

• Homologous Chromosomes: Chromosome pairs, one from each parent, similar in structure and gene content.

• Oogenesis: Process of formation of female gametes in animals.

• Genetic recombination: Process by which alleles are shuffled during meiosis to produce genetic diversity.

• Chromosome condensation: Tight packing of chromosomes visible under a microscope during prophase.

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): The beginning of diplotene is recognised by the dissolution of the synaptonemal complex and formation of X-shaped structures called chiasmata.

Reason(R): In oocytes of some vertebrates, diplotene can last for months or years.

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 and (R) is the correct explanation of (A)

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

Explanation: Both statements are correct. Diplotene begins with dissolution of the synaptonemal complex and chiasmata formation, allowing homologues to separate partially. In vertebrate oocytes, this stage can arrest for extended periods, sometimes months or years, before meiosis resumes. Therefore, the reason does not explain the assertion. Answer: 4

Q1: During which sub-stage of prophase I does crossing over occur?

1. Leptotene

2. Zygotene

3. Pachytene

4. Diakinesis

Explanation: Crossing over occurs during pachytene of prophase I when homologous chromosomes are fully synapsed, allowing recombination at chiasmata. Leptotene involves chromosome condensation, zygotene involves synapsis initiation, and diakinesis involves chromosome separation. Answer: Pachytene. Answer: 3

Q2: Synaptonemal complex is primarily made of:

1. DNA only

2. RNA only

3. Proteins

4. Lipids

Explanation: The synaptonemal complex is a protein structure that forms between homologous chromosomes during meiosis to facilitate pairing and recombination. DNA forms the chromosomes, RNA is not the main component, and lipids are absent. Answer: Proteins. Answer: 3

Q3: Which structure marks the site of genetic exchange in meiosis?

1. Synaptonemal complex

2. Centromere

3. Chiasma

4. Spindle fiber

Explanation: Chiasmata are X-shaped structures where homologous chromosomes exchange genetic material during meiosis, enabling recombination. Synaptonemal complex facilitates pairing, centromeres attach chromosomes to spindles, and spindle fibers separate chromosomes. Answer: Chiasma. Answer: 3

Q4: In which gametogenesis process does prolonged diplotene arrest occur?

1. Spermatogenesis

2. Oogenesis

3. Vegetative propagation

4. Binary fission

Explanation: Prolonged diplotene arrest occurs in oogenesis of vertebrates, where oocytes can remain in this stage for months or years before completing meiosis. Spermatogenesis proceeds continuously. Vegetative propagation and binary fission are asexual and unrelated. Answer: Oogenesis. Answer: 2

Q5: What is the main purpose of crossing over?

1. Chromosome condensation

2. Genetic recombination

3. Spindle formation

4. Cell growth

Explanation: Crossing over facilitates genetic recombination by exchanging alleles between homologous chromosomes, increasing genetic diversity in gametes. Condensation and spindle formation are structural events, while cell growth is unrelated. Answer: Genetic recombination. Answer: 2

Q6: Which meiotic stage immediately follows diplotene?

1. Leptotene

2. Diakinesis

3. Metaphase I

4. Anaphase I

Explanation: Diakinesis follows diplotene, characterized by chromosome condensation, nucleolus disappearance, and chiasmata terminalization. Leptotene is earlier, metaphase I is after prophase I, and anaphase I follows metaphase I. Answer: Diakinesis. Answer: 2

Q7: Assertion (A): Chiasmata hold homologous chromosomes together temporarily.
Reason (R): Crossing over occurs at chiasmata.

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: Chiasmata are points where homologues are physically connected and crossing over occurs. Therefore, both statements are correct, and the reason directly explains the assertion. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match sub-stage with characteristic:

1. Leptotene    A. Synapsis begins
2. Zygotene    B. Chromosomes condense
3. Pachytene    C. Crossing over occurs
4. Diplotene    D. Chiasmata visible

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

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

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

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

Explanation: Leptotene: chromosomes condense; Zygotene: synapsis begins; Pachytene: crossing over occurs; Diplotene: chiasmata visible. This sequence reflects correct meiotic prophase I stages. Answer: 1

Q9: The temporary connection between homologous chromosomes during diplotene is called ______.

1. Centromere

2. Chiasma

3. Spindle fiber

4. Synaptonemal complex

Explanation: Chiasma is the X-shaped connection between homologous chromosomes at sites of crossing over, visible in diplotene. Centromeres connect sister chromatids, spindle fibers separate chromosomes, and synaptonemal complex dissolves at this stage. Answer: Chiasma. Answer: 2

Q10: Select the correct statements:

1. Synaptonemal complex forms during zygotene

2. Chiasmata become visible in diplotene

3. Crossing over occurs in pachytene

4. Diplotene can be prolonged in oocytes

Explanation: All statements are correct. Synaptonemal complex formation begins in zygotene, chiasmata become visible in diplotene, crossing over occurs in pachytene, and diplotene arrest can last months or years in vertebrate oocytes. Answer: 1,2,3,4

Subtopic: Mitosis and Growth

• Mitosis: A type of cell division producing two genetically identical daughter cells.

• Equational division: Another term for mitosis, as chromosome number remains unchanged in daughter cells.

• Genetic stability: Maintenance of chromosome number and genetic content across cell divisions.

• Multicellular organism: Organism composed of multiple cells performing specialized functions.

• Cell cycle: Sequence of events in a cell leading to division and replication.

• Daughter cells: Cells produced by division of a parent cell, genetically identical in mitosis.

• Growth: Increase in cell number or size in an organism.

• Chromosome: DNA-containing structure that carries genetic information.

• Division: Process by which a parent cell produces two or more new cells.

• Specialization: Process where cells develop distinct functions in multicellular organisms.

• Replication: Copying of DNA prior to mitosis to ensure genetic fidelity.

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): The growth of multicellular organism is due to mitosis
Reason (R): Mitosis is also called equational division and it offers genetic stability

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 and (R) is the correct explanation of (A)

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

Explanation: Mitosis leads to growth in multicellular organisms by increasing cell number without altering genetic content. It is termed equational division as daughter cells retain the same chromosome number, ensuring genetic stability. Therefore, both assertion and reason are correct, and reason correctly explains the assertion. Answer: Both (A) and (R) are correct and (R) is the correct explanation of (A). Answer: 3

Q1: During which phase of mitosis do chromosomes align at the cell equator?

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Explanation: In metaphase, chromosomes align along the metaphase plate, preparing for equal segregation. Proper alignment ensures that each daughter cell receives identical genetic material. Prophase is condensation, anaphase is separation, and telophase is nuclear reformation. Answer: Metaphase. Answer: 2

Q2: Mitosis occurs in which type of cells for growth?

1. Germ cells

2. Soma cells

3. Egg cells only

4. All cells including bacteria

Explanation: Mitosis occurs in somatic cells to facilitate growth and repair in multicellular organisms. Germ cells undergo meiosis, and bacteria divide by binary fission. Mitosis maintains genetic consistency in body cells. Answer: Soma cells. Answer: 2

Q3: Which of the following ensures genetic stability during mitosis?

1. Random chromosome segregation

2. DNA replication prior to division

3. Crossing over

4. Independent assortment

Explanation: DNA replication during interphase ensures each daughter cell receives an exact copy of chromosomes. Crossing over and independent assortment occur in meiosis, not mitosis. Accurate replication is crucial for maintaining genetic stability during growth. Answer: DNA replication prior to division. Answer: 2

Q4: Which structure separates sister chromatids during mitosis?

1. Centromere

2. Spindle fibers

3. Cell membrane

4. Nuclear envelope

Explanation: Spindle fibers attach to centromeres and pull sister chromatids apart to opposite poles during anaphase. This ensures equal genetic distribution. Centromere is attachment site, nuclear envelope reforms in telophase, cell membrane divides during cytokinesis. Answer: Spindle fibers. Answer: 2

Q5: Mitosis is essential for which of the following?

1. Growth and repair

2. Genetic recombination

3. Gamete formation

4. Speciation

Explanation: Mitosis produces identical somatic cells, supporting growth, tissue repair, and replacement. Genetic recombination and gamete formation occur in meiosis, not mitosis. It maintains genetic stability, enabling multicellular organisms to grow and maintain tissues. Answer: Growth and repair. Answer: 1

Q6: The phase of mitosis where nuclear envelope reforms is:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Explanation: During telophase, separated chromosomes decondense, and the nuclear envelope reforms around each set, creating two nuclei. This marks the end of mitosis before cytokinesis. Prophase involves condensation, metaphase alignment, anaphase separation. Answer: Telophase. Answer: 4

Q7: Assertion (A): Mitosis is called equational division.
Reason (R): It produces daughter cells with identical chromosome number.

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: Mitosis maintains chromosome number in daughter cells, hence called equational division. Both assertion and reason are correct, and reason explains why mitosis is equational. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the phase of mitosis with its key event:

A. Prophase    1. Chromosomes condense
B. Metaphase    2. Chromosomes align at equator
C. Anaphase    3. Chromatids separate
D. Telophase    4. Nuclear envelope reforms

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: Prophase involves condensation, metaphase alignment, anaphase separation, and telophase nuclear reformation. Matching ensures understanding of sequential mitotic events. Answer: A-1, B-2, C-3, D-4. Answer: 1

Q9: The division that maintains chromosome number in daughter cells is called ______.

1. Meiosis

2. Mitosis

3. Binary fission

4. Conjugation

Explanation: Mitosis produces daughter cells with the same chromosome number as the parent, ensuring genetic stability and supporting growth. Meiosis reduces chromosome number, while binary fission and conjugation occur in prokaryotes. Answer: Mitosis. Answer: 2

Q10: Which statements about mitosis are correct?

1. Produces genetically identical cells

2. Occurs in somatic cells

3. Increases chromosome number in daughter cells

4. Maintains genetic stability

Explanation: Mitosis produces identical cells in somatic tissues, maintaining genetic stability. It does not increase chromosome number; meiosis reduces it. Correct statements are 1, 2, and 4. Answer: 1, 2, 4

Topic: Meiosis
Subtopic: Stages of Prophase I

Keyword Definitions:
- Meiosis: A reductional cell division process producing four haploid gametes from one diploid cell.
- Prophase I: The longest meiotic phase where homologous chromosomes pair and exchange segments.
- Synapsis: Pairing of homologous chromosomes during meiosis.
- Bivalent: A pair of homologous chromosomes held together by synaptonemal complex.
- Crossing Over: Exchange of genetic material between homologous chromosomes, enhancing variation.
- Chiasmata: Visible points where crossing over occurs between homologous chromosomes.
- Leptotene: The first substage where chromosomes start condensing.
- Zygotene: The second substage where homologous chromosomes pair via synapsis.
- Pachytene: The substage where crossing over occurs between chromatids.
- Diplotene: The stage where synaptonemal complex dissolves and homologues separate slightly.

Lead Question - 2022 (Abroad):
In prophase I of meiosis, chromosomes start pairing together and synapsis takes place. This process occurs during which of the following stage?
(1) Pachytene
(2) Diplotene
(3) Leptotene
(4) Zygotene
Explanation: The correct answer is (4). Synapsis or pairing of homologous chromosomes occurs during the zygotene stage of prophase I. During this stage, homologous chromosomes align precisely and form bivalents through the formation of a synaptonemal complex that enables genetic recombination later.

1. Which of the following substage of prophase I is characterized by crossing over?
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Explanation: The correct answer is (c). Crossing over, the exchange of genetic material between homologous chromosomes, occurs during pachytene. This process increases genetic variation and involves breakage and reunion of non-sister chromatids at chiasmata.

2. During which substage of prophase I do chiasmata first appear?
(a) Leptotene
(b) Diplotene
(c) Pachytene
(d) Diakinesis
Explanation: The correct answer is (b). Chiasmata, the visible manifestations of crossing over, appear during diplotene as homologous chromosomes begin to repel each other while remaining attached at crossover sites.

3. The dissolution of the nuclear membrane and disappearance of the nucleolus occur in which phase of meiosis I?
(a) Metaphase I
(b) Prophase I
(c) Anaphase I
(d) Telophase I
Explanation: The correct answer is (b). During the later stages of prophase I, the nuclear envelope disintegrates and the nucleolus disappears, marking the preparation for alignment of homologous chromosomes on the metaphase plate.

4. The structure responsible for holding homologous chromosomes together during synapsis is called:
(a) Centrosome
(b) Synaptonemal complex
(c) Kinetochore
(d) Centriole
Explanation: The correct answer is (b). The synaptonemal complex is a protein structure that forms between homologous chromosomes during zygotene, ensuring precise pairing and alignment required for crossing over in pachytene.

5. The separation of homologous chromosomes occurs during:
(a) Anaphase I
(b) Anaphase II
(c) Telophase I
(d) Metaphase II
Explanation: The correct answer is (a). In anaphase I, homologous chromosomes separate and move to opposite poles. This reductional division halves the chromosome number, producing haploid cells while maintaining sister chromatids attached.

6. During which substage of prophase I does chromosome condensation begin?
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Explanation: The correct answer is (a). Chromosome condensation begins during leptotene. Chromosomes appear as thin, thread-like structures that start preparing for synapsis in the subsequent zygotene stage.

7. Assertion-Reason:
Assertion (A): Crossing over leads to genetic recombination.
Reason (R): It occurs between sister chromatids of the same chromosome.
(a) Both A and R are true, and R explains A
(b) Both A and R are true, but R does not explain A
(c) A is true, but R is false
(d) A is false, but R is true
Explanation: Option (c) is correct. Crossing over causes genetic recombination but occurs between non-sister chromatids of homologous chromosomes, not between sister chromatids. This ensures exchange of genetic material, enhancing genetic diversity.

8. Matching Type:
Match the substage with its event:
(a) Leptotene    (i) Chiasmata appear
(b) Zygotene    (ii) Synapsis begins
(c) Pachytene    (iii) Crossing over occurs
(d) Diplotene    (iv) Chromosomes condense
Options:
(1) a-iv, b-ii, c-iii, d-i
(2) a-ii, b-iv, c-i, d-iii
(3) a-i, b-iii, c-ii, d-iv
(4) a-iv, b-iii, c-i, d-ii
Explanation: The correct option is (1). Leptotene shows chromosome condensation, zygotene shows synapsis, pachytene involves crossing over, and diplotene marks chiasmata appearance as homologues begin to separate partially.

9. Fill in the Blank:
The visible points where crossing over occurs are called ________.
(a) Synapsis
(b) Bivalents
(c) Chiasmata
(d) Centrosomes
Explanation: The correct answer is (c). Chiasmata are visible junctions between homologous chromosomes where crossing over has occurred, seen during diplotene, signifying genetic exchange and recombination.

10. Choose the Correct Statements:
1. Synapsis occurs in zygotene.
2. Crossing over occurs in pachytene.
3. Chiasmata appear in leptotene.
4. Chromosomes condense in leptotene.
(a) 1, 2, and 4
(b) 1 and 3
(c) 2 and 3
(d) 1, 3, and 4
Explanation: Option (a) is correct. Synapsis occurs in zygotene, crossing over in pachytene, and condensation starts in leptotene. Chiasmata, however, appear in diplotene, not in leptotene.

Topic: Meiosis
Subtopic: Phases and Significance of Meiosis

Keyword Definitions:

• Meiosis: A type of cell division that reduces the chromosome number by half, resulting in four haploid daughter cells.

• Homologous chromosomes: Chromosome pairs of the same length, centromere position, and gene sequence, one from each parent.

• Crossing over: Exchange of genetic material between homologous chromosomes during prophase I of meiosis.

• Recombination: The process by which new genetic combinations are produced through crossing over.

• S phase: The synthesis phase of interphase where DNA replication occurs before meiosis I, not meiosis II.

Lead Question – 2022
Regarding Meiosis, which of the statements is incorrect:
(1) DNA replication occurs in S phase of Meiosis-II
(2) Pairing of homologous chromosomes and recombination occurs in Meiosis-I
(3) Four haploid cells are formed at the end of Meiosis-II
(4) There are two stages in Meiosis, Meiosis-I and II

Explanation: DNA replication occurs before Meiosis I, during the S phase of interphase, and not in Meiosis II. Hence, statement (1) is incorrect. The remaining statements are correct, as Meiosis I includes crossing over and Meiosis II results in four haploid daughter cells. Correct answer is (1).

1. The pairing of homologous chromosomes occurs during:
(1) Prophase I
(2) Metaphase I
(3) Anaphase I
(4) Telophase I
Explanation: Pairing of homologous chromosomes (synapsis) occurs during prophase I of meiosis I, leading to crossing over and genetic recombination. Hence, the correct answer is (1).

2. The structure formed by the synapsis of homologous chromosomes is called:
(1) Chiasma
(2) Bivalent
(3) Centromere
(4) Kinetochore
Explanation: When homologous chromosomes pair during prophase I, they form a bivalent or tetrad structure, facilitating genetic recombination. The correct answer is (2).

3. Which of the following occurs only in Meiosis I but not in Meiosis II?
(1) Separation of sister chromatids
(2) Crossing over
(3) Formation of spindle
(4) Alignment of chromosomes
Explanation: Crossing over occurs only during prophase I of meiosis I and not in meiosis II. Hence, the correct answer is (2).

4. During which phase of Meiosis I does crossing over occur?
(1) Leptotene
(2) Pachytene
(3) Diplotene
(4) Zygotene
Explanation: Crossing over occurs in the pachytene stage of prophase I when homologous chromosomes exchange segments. The correct answer is (2).

5. Which of the following statements about Meiosis II is true?
(1) It involves DNA replication
(2) It separates homologous chromosomes
(3) It produces four haploid cells
(4) It results in crossing over
Explanation: Meiosis II is similar to mitosis and involves the separation of sister chromatids to form four haploid cells. Hence, the correct answer is (3).

6. The reduction in chromosome number occurs during:
(1) Prophase II
(2) Anaphase I
(3) Anaphase II
(4) Telophase II
Explanation: Reduction in chromosome number occurs during anaphase I when homologous chromosomes separate, leading to haploid cells. Hence, the correct answer is (2).

7. Assertion (A): Meiosis results in genetic variation.
Reason (R): Crossing over and independent assortment occur during meiosis.
(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: Both are true and the reason correctly explains the assertion, as crossing over and independent assortment generate variation. Hence, the correct answer is (1).

8. Match the following:
A. Crossing over — (i) Pachytene
B. Synapsis — (ii) Zygotene
C. Terminalization — (iii) Diplotene
D. Tetrad — (iv) Bivalent
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: Crossing over occurs in pachytene, synapsis in zygotene, terminalization in diplotene, and tetrad formation represents a bivalent. Hence, the correct answer is (1).

9. Fill in the blank:
During meiosis, DNA replication occurs once but cell division occurs _______.
(1) Once
(2) Twice
(3) Thrice
(4) Four times
Explanation: In meiosis, DNA replication occurs only once before meiosis I, but two divisions (meiosis I and II) occur to form four haploid cells. Hence, the correct answer is (2).

10. Choose the correct statements:
(1) Meiosis maintains chromosome number constant in sexually reproducing organisms.
(2) Crossing over occurs in prophase II.
(3) DNA replication occurs in meiosis II.
(4) Meiosis produces diploid gametes.
Explanation: Meiosis ensures chromosome number stability across generations and genetic diversity through recombination. Crossing over occurs in prophase I, not II. Hence, only statement (1) is correct.

Subtopic: Mitosis

Keyword Definitions:
• Mitosis: Process of eukaryotic cell division producing two genetically identical daughter cells.
• Chromosome: Thread-like structure of DNA and proteins carrying genetic information.
• Centromere: Region of a chromosome where spindle fibers attach.
• Spindle fibers: Microtubules that segregate chromosomes during cell division.
• Telophase: Final stage of mitosis where chromosomes decondense and nuclear envelope reforms.
• Anaphase: Stage where sister chromatids separate toward opposite poles.
• Metaphase: Stage where chromosomes align at the cell equator.
• Daughter cells: Cells resulting from division of a parent cell.
• Equator of cell: Central plane where chromosomes align during metaphase.
• Cell cycle: Series of events from one cell division to the next.

Lead Question (2022):
Select the incorrect statement with reference to mitosis:
(1) Spindle fibres attach to centromere of chromosomes.
(2) Chromosomes decondense at telophase
(3) Splitting of centromere occurs at anaphase
(4) All the chromosomes lie at the equator at metaphase

Explanation: The correct answer is (3). In mitosis, the splitting of the centromere actually occurs at anaphase, which is correct. Therefore, this statement is often misunderstood as incorrect if misinterpreted. The other statements are accurate: spindle fibers attach to centromeres, chromosomes decondense at telophase, and chromosomes align at the equator during metaphase.

Guessed MCQs:

1. Single Correct Answer:
During which phase of mitosis do chromosomes align at the equator?
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
Explanation: The correct answer is (b). In metaphase, spindle fibers attach to centromeres and chromosomes align at the equatorial plate, ensuring proper segregation to daughter cells.

2. Single Correct Answer:
Which structure attaches to spindle fibers during mitosis?
(a) Telomere
(b) Centromere
(c) Chromatid
(d) Nucleolus
Explanation: The correct answer is (b). The centromere is the region where spindle fibers attach, facilitating proper segregation of sister chromatids during mitosis.

3. Single Correct Answer:
Chromosome decondensation occurs during which mitotic phase?
(a) Prophase
(b) Metaphase
(c) Telophase
(d) Anaphase
Explanation: The correct answer is (c). During telophase, chromosomes decondense to form chromatin, and the nuclear envelope reforms around each set of daughter chromosomes.

4. Assertion-Reason MCQ:
Assertion (A): Spindle fibers are essential for chromosome segregation.
Reason (R): They attach to chromosomes at centromeres and pull chromatids to opposite poles.
(a) Both A and R are correct and R explains A
(b) Both A and R are correct but R does not explain A
(c) A is correct, R is incorrect
(d) A is incorrect, R is correct
Explanation: The correct answer is (a). Spindle fibers attach to centromeres and ensure proper separation of chromatids, making them essential for accurate chromosome segregation during mitosis.

5. Single Correct Answer:
During anaphase, what occurs?
(a) Chromosomes condense
(b) Chromatids separate toward poles
(c) Chromosomes align at equator
(d) Nuclear envelope forms
Explanation: The correct answer is (b). In anaphase, sister chromatids separate and move toward opposite poles, ensuring equal genetic distribution to daughter cells.

6. Single Correct Answer:
What is the main purpose of mitosis?
(a) Sexual reproduction
(b) Producing genetically identical daughter cells
(c) Crossing over
(d) Gamete formation
Explanation: The correct answer is (b). Mitosis produces two genetically identical daughter cells for growth, repair, and asexual reproduction in eukaryotic organisms.

7. Matching Type:
Match the mitotic phase with its event:
Column A
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Column B
A. Chromosomes condense
B. Chromosomes align at equator
C. Chromatids separate
D. Nuclear envelope reforms
Options:
(a) 1-A, 2-B, 3-C, 4-D
(b) 1-B, 2-A, 3-D, 4-C
(c) 1-A, 2-C, 3-B, 4-D
(d) 1-D, 2-B, 3-A, 4-C
Explanation: The correct answer is (a). Prophase involves chromosome condensation (1-A), metaphase alignment at equator (2-B), anaphase chromatid separation (3-C), and telophase nuclear envelope formation (4-D).

8. Fill in the Blanks:
During ______, sister chromatids separate and move toward ______.
(a) Anaphase, opposite poles
(b) Metaphase, equator
(c) Telophase, cytoplasm
(d) Prophase, nucleus
Explanation: The correct answer is (a). In anaphase, spindle fibers pull sister chromatids toward opposite poles, ensuring equal distribution of genetic material.

9. Single Correct Answer:
Which phase of mitosis is characterized by the disappearance of the nuclear envelope?
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
Explanation: The correct answer is (a). During prophase, the nuclear envelope breaks down, allowing spindle fibers to interact with chromosomes for proper alignment.

10. Choose the correct statements:
(a) Mitosis produces two identical daughter cells
(b) Spindle fibers attach to centromeres
(c) Chromosomes decondense at telophase
(d) Chromatids separate during metaphase
Explanation: The correct answer is (a), (b), and (c). Chromatid separation occurs in anaphase, not metaphase, making (d) incorrect. Other statements correctly describe events of mitosis.

Topic: Gametogenesis
Subtopic: Spermatogenesis vs Oogenesis

Keyword Definitions:
• Spermatogenesis: Process of formation of haploid sperm from diploid spermatogonia in testes.
• Oogenesis: Process of formation of haploid ovum from diploid oogonia in ovaries.
• Meiosis: Cell division producing haploid gametes with half the chromosome number.
• Haploid gametes: Gametes containing single set of chromosomes (n).
• Luteinising Hormone (LH): Pituitary hormone that triggers testosterone production and ovulation.
• Follicle Stimulating Hormone (FSH): Pituitary hormone stimulating spermatogenesis and follicle maturation.
• Stem cells: Undifferentiated cells capable of mitosis and differentiation.
• Puberty: Developmental stage when reproductive organs mature and gametogenesis begins.
• Differentiation: Process where gametes attain mature functional form.
• Continuous meiosis: Spermatogenesis occurs uninterruptedly post-puberty, unlike oogenesis.

Lead Question (2022):
Which of the following statements are true for spermatogenesis but do not hold true for oogenesis :
(a) It results in the formation of haploid gametes
(b) Differentiation of gamete occurs after the completion of meiosis
(c) Meiosis occurs continuously in a mitotically dividing stem cell population
(d) It is controlled by the Luteinising hormone (LH) and Follicle stimulating Hormone (FSH) secreted by the anterior pituitary
(e) It is initiated at puberty
Choose the most appropriate answer from the options given below:
(1) (b) and (c) only
(2) (b), (d) and (e) only
(3) (b), (c) and (e) only
(4) (c) and (e) only

Explanation: The correct answer is (3). In spermatogenesis, gamete differentiation occurs after meiosis (b), meiosis continues in dividing stem cells (c), and the process begins at puberty (e). These features are distinct from oogenesis, where meiosis is discontinuous and differentiation occurs in the ovum before completion of meiosis.

Guessed MCQs:

1. Single Correct Answer:
Which hormone primarily regulates spermatogenesis?
(a) Estrogen
(b) Testosterone
(c) Progesterone
(d) Prolactin
Explanation: The correct answer is (b). Testosterone, produced by Leydig cells under LH stimulation, is essential for spermatogenesis. FSH also contributes by stimulating Sertoli cells, but testosterone maintains continuous sperm production.

2. Single Correct Answer:
At what stage does oogenesis arrest until puberty?
(a) Primary oocyte
(b) Secondary oocyte
(c) Zygote
(d) Spermatogonia
Explanation: The correct answer is (a). In oogenesis, primary oocytes are arrested in prophase I of meiosis until puberty. This contrasts spermatogenesis, where meiosis occurs continuously after puberty.

3. Single Correct Answer:
Which is a continuous process in males but discontinuous in females?
(a) Spermatogenesis
(b) Oogenesis
(c) Both
(d) Neither
Explanation: The correct answer is (a). Spermatogenesis is continuous post-puberty in males, whereas oogenesis has prolonged meiotic arrest and produces limited gametes over the female reproductive lifespan.

4. Assertion-Reason MCQ:
Assertion (A): Spermatogenesis produces four functional gametes per meiotic cycle.
Reason (R): Oogenesis produces one functional ovum per meiotic cycle.
(a) Both A and R are correct and R explains A
(b) Both A and R are correct but R does not explain A
(c) A is correct, R is false
(d) A is false, R is true
Explanation: The correct answer is (a). Spermatogenesis yields four functional sperms, whereas oogenesis produces only one ovum with polar bodies. R accurately explains the difference in gamete production per meiotic division.

5. Single Correct Answer:
Differentiation of sperm occurs in which part of male reproductive system?
(a) Seminiferous tubules
(b) Epididymis
(c) Vas deferens
(d) Testicular interstitial cells
Explanation: The correct answer is (b). Spermiogenesis, the differentiation of spermatids into mature spermatozoa, occurs in the epididymis, completing the process initiated in the seminiferous tubules.

6. Single Correct Answer:
Which cell population undergoes mitotic divisions in spermatogenesis?
(a) Primary spermatocytes
(b) Spermatogonia
(c) Spermatids
(d) Spermatozoa
Explanation: The correct answer is (b). Spermatogonia are mitotically active stem cells that divide to maintain the stem cell pool and produce primary spermatocytes, which then undergo meiosis.

7. Matching Type:
Match the following:
Column A
1. Spermatogenesis
2. Oogenesis
3. Primary oocyte arrest
4. Gamete differentiation
Column B
A. After meiosis
B. Continuous post-puberty
C. Prophase I
D. Discontinuous
Options:
(a) 1-B, 2-D, 3-C, 4-A
(b) 1-D, 2-B, 3-C, 4-A
(c) 1-B, 2-D, 3-A, 4-C
(d) 1-B, 2-D, 3-D, 4-A
Explanation: The correct answer is (a). Spermatogenesis is continuous post-puberty (1-B), oogenesis is discontinuous (2-D), primary oocytes arrest in prophase I (3-C), and gamete differentiation occurs after meiosis (4-A).

8. Fill in the Blanks:
Spermatogenesis begins at _______ and produces _______ haploid gametes per cycle.
(a) Birth, four
(b) Puberty, four
(c) Puberty, one
(d) Birth, one
Explanation: The correct answer is (b). Spermatogenesis begins at puberty in males and yields four haploid sperm per meiotic cycle, in contrast to oogenesis which produces one ovum.

9. Single Correct Answer:
Which statement is unique to spermatogenesis compared to oogenesis?
(a) Hormonal regulation by LH and FSH
(b) Production of haploid gametes
(c) Continuous meiosis in stem cells
(d) Occurs in gonads
Explanation: The correct answer is (c). Continuous meiosis in mitotically active stem cells (spermatogonia) is unique to spermatogenesis. Oogenesis involves discontinuous meiosis with long meiotic arrest periods.

10. Choose the correct statements:
(a) Spermatogenesis is continuous
(b) Oogenesis produces four ovum
(c) Meiosis starts at puberty in males
(d) Differentiation occurs post-meiosis in spermatogenesis
Options:
1. a, c, d only
2. a and b only
3. b and d only
4. All statements
Explanation: The correct answer is (1). Spermatogenesis is continuous (a), meiosis begins at puberty in males (c), and differentiation occurs after meiosis (d). Oogenesis produces only one ovum, so statement (b) is incorrect.

Topic: Structure of Chromosomes
Subtopic: Types of Chromosomes Based on Centromere Position

Keyword Definitions:

• Chromosome: Thread-like structure made of DNA and proteins carrying genetic information.

• Centromere: The constricted region of a chromosome where spindle fibers attach during cell division.

• Metacentric Chromosome: Centromere lies in the middle forming two equal arms.

• Sub-metacentric Chromosome: Centromere slightly away from the center forming unequal arms.

• Acrocentric Chromosome: Centromere near one end forming one long and one short arm.

• Telocentric Chromosome: Centromere located at the terminal end, forming a single arm.

Lead Question (2022):
Match List–I with List–II.
List – I           List – II
(a) Metacentric           (i) Centromere situated close to the end forming one extremely short and one very long arm
(b) Acrocentric           (ii) Centromere at the terminal end
(c) Sub-metacentric           (iii) Centromere in the middle forming equal arms
(d) Telocentric           (iv) Centromere slightly away from the middle forming unequal arms
(1) (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
(2) (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
(3) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
(4) (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation: Metacentric chromosomes have centromere in the middle, sub-metacentric slightly away from the center, acrocentric near the end, and telocentric at the terminal end. Hence, the correct answer is (3) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii).

1. Guessed Question:
The centromere is located exactly in the middle in:
(1) Acrocentric chromosome
(2) Metacentric chromosome
(3) Sub-metacentric chromosome
(4) Telocentric chromosome

Explanation: In metacentric chromosomes, the centromere lies in the center forming two equal arms, giving a ‘V’ shape during anaphase. Hence, the correct answer is (2) Metacentric chromosome.

2. Guessed Question:
Which type of chromosome has the centromere near one end, producing one short and one long arm?
(1) Telocentric
(2) Metacentric
(3) Sub-metacentric
(4) Acrocentric

Explanation: Acrocentric chromosomes have the centromere near one end, resulting in one extremely short and one long arm, forming a ‘J’ shape. Hence, the correct answer is (4) Acrocentric.

3. Guessed Question:
Sub-metacentric chromosomes have arms that are:
(1) Equal in length
(2) Unequal in length
(3) Without arms
(4) Circular in structure

Explanation: Sub-metacentric chromosomes have the centromere slightly away from the center, forming one shorter and one longer arm. Hence, the correct answer is (2) Unequal in length.

4. Guessed Question:
Telocentric chromosomes are found in:
(1) Humans
(2) Mice
(3) Plants only
(4) Bacteria

Explanation: Telocentric chromosomes have centromeres at the terminal end, forming only one arm. They are common in mice but not in humans. Hence, the correct answer is (2) Mice.

5. Guessed Question:
Which chromosome type appears ‘V’-shaped during anaphase?
(1) Metacentric
(2) Sub-metacentric
(3) Acrocentric
(4) Telocentric

Explanation: Metacentric chromosomes have centromeres in the middle, resulting in a V-shape during anaphase movement as both arms are equal. Hence, the correct answer is (1) Metacentric.

6. Guessed Question:
The term “centromere” refers to:
(1) End region of chromosome
(2) Primary constriction region
(3) Tip of the chromatid
(4) Region where crossing over occurs

Explanation: Centromere is the primary constriction on a chromosome that holds sister chromatids together and attaches to spindle fibers during cell division. Hence, the correct answer is (2) Primary constriction region.

7. Assertion-Reason Question:
Assertion (A): The shape of a chromosome during anaphase depends on centromere position.
Reason (R): The centromere attaches to spindle fibers, pulling chromatids apart.
(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: Chromosome shape at anaphase (V, L, J, or I) is determined by centromere position. Centromeres connect spindle fibers for separation. Hence, both statements are true, and R explains A. The correct answer is (1).

8. Matching Type Question:
Match chromosome type with its shape at anaphase:
A. Metacentric — (i) V-shaped
B. Sub-metacentric — (ii) L-shaped
C. Acrocentric — (iii) J-shaped
D. Telocentric — (iv) I-shaped
(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: Metacentric chromosomes are V-shaped, sub-metacentric L-shaped, acrocentric J-shaped, and telocentric I-shaped. Hence, the correct answer is (1) A–i, B–ii, C–iii, D–iv.

9. Fill in the Blanks:
The position of the ______ determines the shape of chromosomes during ______.
(1) Nucleolus, prophase
(2) Centromere, anaphase
(3) Spindle fiber, metaphase
(4) Chromatid, telophase

Explanation: Centromere position decides the shape of chromosomes at anaphase. V, L, J, or I shapes appear based on centromere location. Hence, the correct answer is (2) Centromere, anaphase.

10. Choose the Correct Statements:
(a) Centromere position determines chromosome type.
(b) Metacentric chromosomes form equal arms.
(c) Telocentric chromosomes have no short arm.
(d) Acrocentric chromosomes form equal arms.
(1) (a), (b), and (c) only
(2) (b) and (d) only
(3) (a), (c), and (d) only
(4) (a), (b), and (d) only

Explanation: Centromere position defines chromosome type. Metacentric chromosomes have equal arms, telocentric lack short arm, while acrocentric have unequal arms. Hence, the correct answer is (1) (a), (b), and (c) only.

Topic: Meiosis and Genetic Recombination
Subtopic: Recombination Nodules and Crossing Over

Keyword Definitions:

• Recombination nodules: Protein structures on synaptonemal complex indicating sites of crossing over between homologous chromosomes.

• Homologous chromosomes: Chromosome pairs, one from each parent, similar in shape, size, and gene sequence.

• Bivalent: Paired homologous chromosomes during meiosis I.

• Crossing over: Exchange of genetic material between homologous chromosomes during prophase I.

• Terminalization: Process where chiasmata move towards chromosome ends during late prophase I.

• Synaptonemal complex: Protein structure holding homologous chromosomes together during prophase I.

• Chiasmata: Physical points where crossing over occurs.

• Meiosis: Cell division producing four haploid gametes from one diploid cell.

• Genetic recombination: Exchange of genetic material resulting in new allele combinations.

• Prophase I: First stage of meiosis where homologous chromosomes pair and recombination occurs.

Lead Question (2022)
The appearance of recombination nodules on homologous chromosomes during meiosis characterizes :
(1) Bivalent
(2) Sites at which crossing over occurs
(3) Terminalization
(4) Synaptonemal complex

Explanation:
Recombination nodules appear on the synaptonemal complex at sites where crossing over occurs between homologous chromosomes during prophase I of meiosis. These nodules indicate active genetic recombination. Bivalent refers to paired homologs, and terminalization is chiasmata movement. Correct answer is (2).

1. Single Correct Answer MCQ:
During which substage of prophase I do recombination nodules first appear?
(1) Leptotene
(2) Zygotene
(3) Pachytene
(4) Diplotene

Explanation:
Recombination nodules first appear during the pachytene stage of prophase I when homologous chromosomes are fully synapsed. This marks active crossing over. Leptotene, zygotene, and diplotene stages do not show nodules. Correct answer is (3).

2. Single Correct Answer MCQ:
Which structure physically holds homologous chromosomes together during recombination?
(1) Centromere
(2) Synaptonemal complex
(3) Spindle fibers
(4) Chiasmata

Explanation:
The synaptonemal complex is a protein structure that holds homologous chromosomes together during prophase I, allowing recombination. Chiasmata are points of crossing over but appear after synaptonemal complex formation. Correct answer is (2).

3. Single Correct Answer MCQ:
Chiasmata are observed during:
(1) Metaphase II
(2) Anaphase I
(3) Diplotene of prophase I
(4) Telophase II

Explanation:
Chiasmata, the physical manifestation of crossing over, are observed during the diplotene stage of prophase I. They hold homologous chromosomes together before separation. Correct answer is (3).

4. Single Correct Answer MCQ:
Terminalization refers to:
(1) Formation of recombination nodules
(2) Movement of chiasmata towards chromosome ends
(3) Separation of sister chromatids
(4) Spindle fiber attachment

Explanation:
Terminalization is the movement of chiasmata towards chromosome ends during late prophase I, preparing for segregation. It does not involve nodule formation or spindle attachment. Correct answer is (2).

5. Single Correct Answer MCQ:
A bivalent is formed by:
(1) Two sister chromatids
(2) Two homologous chromosomes
(3) Two unrelated chromosomes
(4) Two chromatids from different cells

Explanation:
A bivalent consists of two homologous chromosomes paired during prophase I of meiosis. Sister chromatids alone do not form a bivalent. Correct answer is (2).

6. Single Correct Answer MCQ:
Recombination nodules indicate:
(1) DNA replication sites
(2) Crossing over sites
(3) Spindle assembly points
(4) Centromere duplication sites

Explanation:
Recombination nodules mark sites where genetic material is exchanged between homologous chromosomes. They are not involved in DNA replication or spindle assembly. Correct answer is (2).

7. Assertion-Reason MCQ:
Assertion (A): Recombination nodules are essential for genetic diversity.
Reason (R): They mark sites where homologous chromosomes exchange genetic material during meiosis.
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:
Recombination nodules facilitate genetic recombination, creating new allele combinations, which is crucial for diversity. Both assertion and reason are correct, and R explains A. Correct answer is (1).

8. Matching Type MCQ:
Match the meiosis feature with description:
A. Pachytene — 1. Chromosomes condense
B. Diplotene — 2. Chiasmata visible
C. Zygotene — 3. Homolog pairing begins
D. Leptotene — 4. Recombination nodules appear
Options:
(1) A–4, B–2, C–3, D–1
(2) A–1, B–2, C–3, D–4
(3) A–4, B–3, C–2, D–1
(4) A–2, B–4, C–3, D–1

Explanation:
During leptotene chromosomes condense, zygotene homologs pair, pachytene recombination nodules appear, and diplotene chiasmata become visible. Correct answer is (1).

9. Fill in the Blanks MCQ:
_________ is the stage when homologous chromosomes are fully synapsed and crossing over occurs.
(1) Zygotene
(2) Pachytene
(3) Leptotene
(4) Diplotene

Explanation:
Pachytene is the prophase I stage when homologous chromosomes are fully synapsed and recombination nodules facilitate crossing over. Correct answer is (2).

10. Choose the correct statements MCQ:
(a) Recombination nodules appear on synaptonemal complex
(b) Crossing over generates genetic variation
(c) Bivalents consist of two homologous chromosomes
(d) Terminalization occurs before pachytene
Options:
(1) a, b, c only
(2) a, c, d only
(3) b, c, d only
(4) a, b, d only

Explanation:
Recombination nodules appear on synaptonemal complex (a), crossing

Topic: Cell Cycle and Mitosis
Subtopic: Events in Mitosis

Keyword Definitions:

• Mitosis: Type of cell division where one cell divides to produce two genetically identical daughter cells.

• Centrioles: Cylindrical structures in animal cells that help in spindle formation during mitosis.

• Chromatids: Two identical halves of a duplicated chromosome joined at the centromere.

• Homologous Chromosomes: Pair of chromosomes, one from each parent, carrying similar genes.

• Spindle Fibres: Microtubules that attach to chromosomes and help separate them during mitosis.

• Kinetochore: Protein structure on a chromosome where spindle fibres attach during cell division.

• Condensation: Coiling and compacting of chromosomes to make them visible under a microscope.

• Cell Division: Process where a parent cell divides into two or more daughter cells.

• Chromosome: DNA molecule with associated proteins carrying genetic information.

• Daughter Cells: Cells produced as a result of cell division, genetically identical in mitosis.

Lead Question (2022)
Which one of the following never occurs during mitotic cell division?
(1) Movement of centrioles towards opposite poles
(2) Pairing of homologous chromosomes
(3) Coiling and condensation of the chromatids
(4) Spindle fibres attach to kinetochores of chromosomes

Explanation:
During mitosis, centrioles move to opposite poles, chromatids coil and condense, and spindle fibres attach to kinetochores. Pairing of homologous chromosomes occurs only in meiosis, not mitosis. Therefore, the event that never occurs in mitosis is (2).

1. Single Correct Answer MCQ:
During mitosis, which phase involves separation of sister chromatids?
(1) Prophase
(2) Metaphase
(3) Anaphase
(4) Telophase

Explanation:
Sister chromatids are separated during anaphase when spindle fibres pull them toward opposite poles. Prophase involves chromosome condensation, metaphase aligns chromosomes at the equator, and telophase involves nuclear envelope formation. Correct answer is (3).

2. Single Correct Answer MCQ:
Which structure organizes spindle fibres during mitosis?
(1) Centrioles
(2) Nucleolus
(3) Plasma membrane
(4) Golgi apparatus

Explanation:
Centrioles organize spindle fibres during mitosis, ensuring proper segregation of chromosomes. The nucleolus, plasma membrane, and Golgi apparatus are not directly involved in spindle formation. Correct answer is (1).

3. Single Correct Answer MCQ:
Chromosome condensation occurs during:
(1) Interphase
(2) Prophase
(3) Cytokinesis
(4) G1 phase

Explanation:
During prophase, chromosomes condense and become visible under a microscope, which facilitates their movement during mitosis. Interphase and G1 are preparatory phases, and cytokinesis divides the cytoplasm. Correct answer is (2).

4. Single Correct Answer MCQ:
The kinetochore is located at:
(1) Chromatid tip
(2) Centromere
(3) Chromosome end
(4) Nucleolus

Explanation:
The kinetochore is a protein structure on the centromere of each chromosome where spindle fibres attach to pull sister chromatids apart. Correct answer is (2).

5. Single Correct Answer MCQ:
Which phase of mitosis follows metaphase?
(1) Prophase
(2) Anaphase
(3) Telophase
(4) Interphase

Explanation:
After metaphase, sister chromatids separate and move to opposite poles during anaphase. Prophase precedes metaphase, telophase follows anaphase, and interphase occurs before mitosis. Correct answer is (2).

6. Single Correct Answer MCQ:
Which event is unique to meiosis and not seen in mitosis?
(1) Chromosome condensation
(2) Spindle fibre attachment
(3) Pairing of homologous chromosomes
(4) Centriole movement

Explanation:
Pairing of homologous chromosomes occurs only in meiosis I (prophase I) to allow crossing over. Chromosome condensation, spindle attachment, and centriole movement occur in both mitosis and meiosis. Correct answer is (3).

7. Assertion-Reason MCQ:
Assertion (A): Spindle fibres attach to kinetochores during mitosis.
Reason (R): Kinetochores are protein complexes on centromeres that facilitate chromatid movement.
Options:
(1) Both A and R correct, R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both A and R incorrect

Explanation:
During mitosis, spindle fibres attach to kinetochores at the centromere, which serve as sites for chromatid movement to opposite poles. Both the assertion and reason are correct, and the reason explains the assertion. Correct answer is (1).

8. Matching Type MCQ:
Match the mitotic event with its phase:
A. Chromosome condensation — 1. Metaphase
B. Sister chromatids separation — 2. Anaphase
C. Nuclear envelope reformation — 3. Telophase
D. Chromosomes align at equator — 4. Prophase
Options:
(1) A–4, B–2, C–3, D–1
(2) A–1, B–2, C–4, D–3
(3) A–4, B–1, C–2, D–3
(4) A–2, B–1, C–3, D–4

Explanation:
In mitosis, chromosomes condense in prophase (A–4), sister chromatids separate in anaphase (B–2), nuclear envelope reforms in telophase (C–3), and chromosomes align at metaphase plate (D–1). Correct answer is (1).

9. Fill in the Blanks MCQ:
During ________, sister chromatids are pulled apart to opposite poles.
(1) Prophase
(2) Anaphase
(3) Telophase
(4) Interphase

Explanation:
Anaphase is the mitotic phase when spindle fibres pull sister chromatids apart to opposite poles, ensuring each daughter cell receives an identical set of chromosomes. Correct answer is (2).

10. Choose the correct statements MCQ:
(a) Centrioles move to opposite poles
(b) Homologous chromosomes pair
(c) Spindle fibres attach to kinetochores
(d) Chromosomes condense
Options:
(1) a, c, d only
(2) a, b only
(3) b, c only
(4) a, b, c, d

Explanation:
In mitosis, centrioles move to opposite poles (a), spindle fibres attach to kinetochores (c), and chromosomes condense (d). Homologous chromosomes pairing (b) occurs only in meiosis. Correct answer is (1).

Topic: Cell Cycle Events
Subtopic: Centriole Duplication

Keyword Definitions:

• Centriole: Cylindrical cell structure involved in spindle formation during cell division.

• S-phase: Phase of cell cycle where DNA replication and centriole duplication occur.

• Prophase: Mitotic stage where chromosomes condense and spindle forms.

• Metaphase: Stage where chromosomes align at the equatorial plate.

• G2 phase: Gap phase before mitosis, preparing for cell division.

Lead Question - 2021

The centriole undergoes duplication during

(1) Prophase
(2) Metaphase
(3) G2 phase
(4) S-phase

Explanation: Centriole duplication occurs during the S-phase of the cell cycle, alongside DNA replication. Each centriole pair duplicates to ensure both daughter cells receive centrosomes for spindle formation. This coordination ensures proper chromosome segregation and genetic stability. Thus, the correct answer is option (4) S-phase.

1. In which phase do chromosomes align at the equator?
(1) Prophase
(2) Anaphase
(3) Metaphase
(4) Telophase
Explanation: Chromosomes align at the equator of the spindle during metaphase. This ensures equal segregation into daughter cells during anaphase. The metaphase plate is a critical checkpoint in mitosis. Thus, the correct answer is option (3) Metaphase.

2. Crossing over occurs in which stage of meiosis?
(1) Zygotene
(2) Diplotene
(3) Pachytene
(4) Leptotene
Explanation: Crossing over occurs in pachytene of prophase I during meiosis. It involves exchange of genetic material between non-sister chromatids of homologous chromosomes, increasing variation. This recombination is vital for evolution and heredity. Thus, the correct answer is option (3) Pachytene.

3. Which stage of mitosis involves nuclear envelope breakdown?
(1) Telophase
(2) Prophase
(3) Metaphase
(4) Anaphase
Explanation: During prophase, the nuclear envelope begins disintegration, chromosomes condense, and spindle fibers appear. This prepares the cell for metaphase alignment. Without this step, chromosomes cannot interact with spindle fibers. Thus, the correct answer is option (2) Prophase.

4. Cytokinesis in plant cells occurs by:
(1) Furrow method
(2) Cell plate formation
(3) Binary fission
(4) Budding
Explanation: Plant cells undergo cytokinesis by cell plate formation due to rigid cell walls. The Golgi vesicles fuse at the equator, forming a new cell wall between daughter cells. This contrasts with furrow method in animal cells. Thus, the correct answer is option (2) Cell plate formation.

5. The spindle apparatus is mainly composed of:
(1) Actin filaments
(2) Intermediate filaments
(3) Microtubules
(4) Collagen fibers
Explanation: The spindle apparatus is composed of microtubules formed from tubulin proteins. These structures attach to kinetochores and help segregate chromosomes. Their dynamic instability ensures proper pull and separation. Thus, the correct answer is option (3) Microtubules.

6. Which checkpoint ensures DNA replication is complete?
(1) G1 checkpoint
(2) G2 checkpoint
(3) Metaphase checkpoint
(4) Cytokinesis checkpoint
Explanation: The G2 checkpoint ensures that DNA replication in S-phase has been completed correctly without errors. This prevents entry into mitosis with damaged or incomplete DNA. It is crucial for genetic stability. Thus, the correct answer is option (2) G2 checkpoint.

7. Assertion-Reason Question:
Assertion (A): Spindle fibers attach to centromeres.
Reason (R): They attach through kinetochore proteins.
(1) Both A and R are true, R is correct explanation of A
(2) Both A and R are true, R is not correct explanation of A
(3) A true, R false
(4) A false, R true
Explanation: Spindle fibers attach to centromeres via kinetochore proteins, ensuring proper segregation. Both statements are true, and R correctly explains A. Thus, the correct answer is option (1).

8. Matching Type Question:
Match the following stages with events:
A. Anaphase - 1. Chromosome alignment
B. Telophase - 2. Chromosome separation
C. Metaphase - 3. Nuclear envelope reformation
D. Prophase - 4. Chromosome condensation
(1) A-2, B-3, C-1, D-4
(2) A-3, B-4, C-2, D-1
(3) A-4, B-2, C-3, D-1
(4) A-1, B-2, C-3, D-4
Explanation: Anaphase involves chromosome separation, telophase involves nuclear reformation, metaphase involves alignment, and prophase involves condensation. Thus, the correct matching is A-2, B-3, C-1, D-4. The correct answer is option (1).

9. Fill in the Blanks:
The protein complex that regulates the cell cycle is called __________.
(1) Tubulin
(2) Cyclin-CDK complex
(3) Actomyosin
(4) Kinetochores
Explanation: Cyclin-CDK complex regulates progression of the cell cycle by phosphorylating target proteins. Different cyclins function at specific phases, ensuring orderly progression. This ensures proper timing of events. Thus, the correct answer is option (2) Cyclin-CDK complex.

10. Choose the correct statements:
(a) Mitosis occurs in somatic cells.
(b) Meiosis occurs only in germ cells.
(c) Mitosis leads to genetic variation.
(d) Meiosis reduces chromosome number by half.
(1) a, b, d
(2) a, c, d
(3) b, c, d
(4) a, b, c, d
Explanation: Mitosis occurs in somatic cells for growth, meiosis occurs in germ cells for gamete formation, and meiosis halves chromosome number. Mitosis maintains genetic stability, not variation. Thus, correct statements are (a), (b), and (d). Correct answer is option (1).

Subtopic: Prophase I Stages

• Meiosis: A type of cell division producing four haploid daughter cells from a diploid cell.

• Prophase I: The first stage of meiosis where homologous chromosomes pair and exchange genetic material.

• Chiasmata: X-shaped structures formed by crossing over of homologous chromosomes.

• Terminalisation: Movement of chiasmata toward the ends of chromosomes.

• Zygotene: Stage where homologous chromosomes begin pairing (synapsis).

• Pachytene: Stage where crossing over occurs between homologous chromosomes.

• Diplotene: Stage where homologous chromosomes begin to separate but chiasmata remain.

• Diakinesis: Final stage of prophase I with terminalisation of chiasmata and preparation for metaphase I.

• Leptotene: Initial stage where chromosomes condense and become visible.

• Homologous chromosomes: Chromosome pairs of similar size and gene sequence, one from each parent.

• Haploid: Cell containing a single set of chromosomes.

Lead Question - 2021

Which stage of meiotic prophase shows terminalisation of chiasmata as its distinctive feature?

(1) Zygotene
(2) Diakinesis
(3) Pachytene
(4) Leptotene

Explanation: Terminalisation of chiasmata is characteristic of diakinesis, the final stage of prophase I, where chiasmata move to chromosome ends in preparation for metaphase I. Answer: Diakinesis.

1. Single Correct Answer MCQ: During which stage does crossing over occur?
Options:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diakinesis

Explanation: Crossing over occurs during the pachytene stage of prophase I when homologous chromosomes exchange segments. Answer: Pachytene.

2. Single Correct Answer MCQ: In which stage do homologous chromosomes begin pairing?
Options:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diplotene

Explanation: Homologous chromosomes start synapsis during zygotene. Answer: Zygotene.

3. Single Correct Answer MCQ: Initial condensation of chromosomes occurs in which stage?
Options:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diakinesis

Explanation: Chromosomes condense and become visible in leptotene. Answer: Leptotene.

4. Single Correct Answer MCQ: Stage where homologous chromosomes separate but remain connected at chiasmata is:
Options:
A. Diplotene
B. Pachytene
C. Zygotene
D. Leptotene

Explanation: Diplotene is when homologous chromosomes separate but chiasmata remain, maintaining genetic linkage. Answer: Diplotene.

5. Single Correct Answer MCQ: The stage that precedes metaphase I in meiosis is:
Options:
A. Pachytene
B. Diplotene
C. Diakinesis
D. Zygotene

Explanation: Diakinesis is the final prophase I stage, preparing chromosomes for metaphase I. Answer: Diakinesis.

6. Single Correct Answer MCQ: Terminalisation of chiasmata ensures:
Options:
A. Chromosome condensation
B. Proper segregation of homologs
C. Synapsis
D. Crossing over

Explanation: Terminalisation moves chiasmata toward chromosome ends, ensuring proper segregation during anaphase I. Answer: Proper segregation of homologs.

7. Assertion-Reason MCQ:
Assertion (A): Diakinesis shows terminalisation of chiasmata.
Reason (R): Chiasmata allow separation of homologous chromosomes.
Options:
A. Both A and R true, R correct explanation
B. Both A and R true, R not correct explanation
C. A true, R false
D. A false, R true

Explanation: Terminalisation occurs in diakinesis, and chiasmata help homologous chromosomes separate. Both A and R are true, and R explains A. Answer: Both A and R true, R correct explanation.

8. Matching Type MCQ:
Column I: 1. Leptotene 2. Zygotene 3. Pachytene 4. Diakinesis
Column II: A. Chromosome condensation B. Synapsis C. Crossing over D. Terminalisation
Options:
A. 1-A, 2-B, 3-C, 4-D
B. 1-B, 2-A, 3-D, 4-C
C. 1-A, 2-C, 3-B, 4-D
D. 1-D, 2-C, 3-B, 4-A

Explanation: Leptotene condenses chromosomes, zygotene for synapsis, pachytene shows crossing over, diakinesis shows terminalisation. Answer: 1-A, 2-B, 3-C, 4-D.

9. Fill in the Blank MCQ: The stage of prophase I in which chiasmata move to chromosome ends is ______.
Options:
A. Pachytene
B. Diakinesis
C. Diplotene
D. Leptotene

Explanation: In diakinesis, chiasmata terminalise, preparing chromosomes for metaphase I. Answer: Diakinesis.

10. Choose the correct statements MCQ:
(a) Zygotene is for synapsis.
(b) Pachytene is for crossing over.
(c) Leptotene shows terminalisation.
(d) Diakinesis shows terminalisation of chiasmata.
Options:
1. (a), (b), (d) only
2. (a), (c), (d) only
3. (b), (c), (d) only
4. All of the above

Subtopic: DNA Replication and Interphase

• Chromosome: Thread-like structure of nucleic acids and proteins carrying genetic information.

• Interphase: Phase of the cell cycle where the cell grows and DNA is replicated, including G1, S, and G2 phases.

• G1 phase: First growth phase after cell division where cell enlarges and performs normal functions.

• S phase: Synthesis phase where DNA replication occurs, doubling the DNA content.

• G2 phase: Second growth phase preparing cell for mitosis.

• Mitosis: Process of nuclear division producing two identical daughter cells.

• 2n: Diploid number representing two sets of chromosomes.

• Fruit fly: Drosophila melanogaster, a model organism in genetics.

• DNA replication: Process of copying DNA before cell division.

• Daughter cells: Cells produced after mitosis, identical to parent cell.

• Chromatid: Each of the two DNA copies in a duplicated chromosome.

Lead Question - 2021

The fruit fly has 8 chromosomes (2n) in each cell. During interphase of Mitosis if the number of chromosomes at G1 phase is 8, what would be the number of chromosomes after S phase?

(1) 16
(2) 4
(3) 32
(4) 8

Explanation: During the S phase of interphase, DNA is replicated but the chromosome number remains the same. Each chromosome now consists of two sister chromatids. Hence, the number of chromosomes after S phase remains 8. Answer: 8.

1. Single Correct Answer MCQ: In which phase does DNA replication occur?
Options:
A. G1 phase
B. S phase
C. G2 phase
D. Mitosis

Explanation: DNA replication occurs during the S phase of interphase, producing two sister chromatids per chromosome while the chromosome number remains unchanged. Answer: S phase.

2. Single Correct Answer MCQ: The diploid number in fruit fly somatic cells is:
Options:
A. 4
B. 8
C. 16
D. 32

Explanation: Fruit fly somatic cells have 8 chromosomes (2n), consisting of two sets of four chromosomes each. Answer: 8.

3. Single Correct Answer MCQ: How many chromatids are present after S phase if chromosome number is 8?
Options:
A. 8
B. 16
C. 32
D. 4

Explanation: After S phase, each of the 8 chromosomes has 2 sister chromatids, making 16 chromatids in total. Answer: 16.

4. Single Correct Answer MCQ: During which phase does cell growth occur without DNA replication?
Options:
A. G1 phase
B. S phase
C. G2 phase
D. Mitosis

Explanation: In the G1 phase, the cell grows and performs metabolic activities without DNA replication. Answer: G1 phase.

5. Single Correct Answer MCQ: Number of chromosomes in a fruit fly daughter cell after mitosis is:
Options:
A. 4
B. 8
C. 16
D. 32

Explanation: Mitosis produces two identical daughter cells, each maintaining the diploid chromosome number of 8. Answer: 8.

6. Single Correct Answer MCQ: Sister chromatids are separated during:
Options:
A. G1 phase
B. S phase
C. Anaphase of mitosis
D. Prophase

Explanation: During anaphase of mitosis, sister chromatids are pulled apart to opposite poles of the cell. Answer: Anaphase of mitosis.

7. Assertion-Reason MCQ:
Assertion (A): Chromosome number doubles after S phase.
Reason (R): DNA is replicated in S phase.
Options:
A. Both A and R true, R correct explanation
B. Both A and R true, R not correct explanation
C. A true, R false
D. A false, R true

Explanation: DNA is replicated in S phase but the chromosome number remains the same; only chromatids double. Answer: A false, R true.

8. Matching Type MCQ:
Column I: 1. DNA replication 2. Cell growth 3. Chromatids number doubles 4. Mitosis produces
Column II: A. S phase B. G1 phase C. 16 chromatids D. Two daughter cells
Options:
A. 1-A, 2-B, 3-C, 4-D
B. 1-B, 2-A, 3-D, 4-C
C. 1-A, 2-C, 3-B, 4-D
D. 1-C, 2-B, 3-A, 4-D

Explanation: DNA replication occurs in S phase, cell growth in G1, sister chromatids double giving 16 chromatids, and mitosis produces two daughter cells. Answer: 1-A, 2-B, 3-C, 4-D.

9. Fill in the Blank MCQ: The phase following G1 and preceding G2 where DNA is duplicated is ______.
Options:
A. M phase
B. S phase
C. Cytokinesis
D. Prophase

Explanation: The S phase is the DNA synthesis phase, occurring after G1 and before G2, duplicating the genetic material for mitosis. Answer: S phase.

10. Choose the correct statements MCQ:
(a) G1 phase is for cell growth.
(b) DNA replication occurs in S phase.
(c) Chromosome number doubles after S phase.
(d) Mitosis produces identical daughter cells.
Options:
1. (a), (b), (d) only
2. (a), (c), (d) only
3. (b), (c), (d) only
4. All of the above

Explanation: G1 is for growth, S phase replicates DNA, chromosome number remains same, and mitosis produces identical cells. Statements (a), (b), and (d) are correct. Answer: (a), (b), (d) only.

Subtopic: Phases of Cell Cycle and Protein Synthesis

• Cell Cycle: Sequence of events in a cell leading to its division and duplication.

• S Phase: Phase of DNA synthesis during interphase.

• G1 Phase: First gap phase, cell grows and prepares for DNA replication.

• G2 Phase: Second gap phase, preparation for mitosis with protein synthesis.

• Quiescent Stage (G0): Non-dividing, inactive phase of the cell cycle.

• Mitosis: Nuclear division producing two identical daughter cells.

• Protein Synthesis: Process of translating genetic code into functional proteins.

• Interphase: Phase between cell divisions including G1, S, and G2.

• Cell Growth: Increase in cell size and organelle number during interphase.

• Replication Initiation: Starting point of DNA duplication during S phase.

• Cell Cycle Checkpoints: Control mechanisms ensuring proper progression of cell division.

Lead Question - 2021

Match List - I with List - II.

List - I
(a) Proteins are synthesized
(b) G2 phase
(c) Quiescent stage
(d) G1 phase

List - II
(i) S phase
(ii) Inactive phase
(iii) Mitosis and initiation of DNA replication
(iv) DNA replication

Options:
A. (iv) (ii) (iii) (i)
B. (iv) (i) (ii) (iii)
C. (ii) (iv) (iii) (i)
D. (iii) (ii) (i) (iv)

Explanation: Proteins are mainly synthesized during G2 phase, which is the preparatory phase for mitosis. G1 is the growth phase before DNA replication (S phase). Quiescent stage (G0) is inactive, and S phase is for DNA replication. Correct matching: (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii). Answer: B.

1. During which phase does DNA replication occur?
Options:
A. G1
B. S phase
C. G2
D. Mitosis

Explanation: DNA replication occurs during S phase of interphase. The cell duplicates its genetic material in preparation for division. G1 is for cell growth, G2 is protein synthesis, and mitosis is nuclear division. Answer: S phase.

2. Which phase is called the quiescent or resting stage?
Options:
A. G0
B. G1
C. S
D. G2

Explanation: The G0 phase is a quiescent stage where cells exit the cell cycle and stop dividing. Cells may remain metabolically active but do not prepare for DNA replication or mitosis. Answer: G0.

3. Proteins for mitosis are synthesized mainly during which phase?
Options:
A. G1
B. S
C. G2
D. Mitosis

Explanation: During G2 phase, the cell synthesizes proteins and organelles needed for mitosis. This ensures readiness for division and proper chromosome segregation. Answer: G2.

4. G1 phase is characterized by:
Options:
A. DNA replication
B. Cell growth
C. Mitotic division
D. Protein degradation

Explanation: G1 phase is the first gap phase of interphase, during which cells grow, synthesize RNA and proteins, and prepare for DNA replication. Answer: Cell growth.

5. During which phase do chromosomes condense and become visible?
Options:
A. G1
B. S
C. G2
D. Mitosis

Explanation: Chromosomes condense and become visible under a microscope during mitosis. This allows proper segregation of genetic material into daughter cells. Answer: Mitosis.

6. Which phase directly follows DNA replication?
Options:
A. G1
B. G2
C. Mitosis
D. G0

Explanation: After DNA replication in S phase, the cell enters G2 phase, where it prepares for mitosis by synthesizing proteins and checking DNA integrity. Answer: G2.

7. Assertion-Reason:
Assertion (A): G1 phase is crucial for cell growth.
Reason (R): G1 phase precedes DNA replication in S phase.
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: G1 phase is critical for cell growth, RNA, and protein synthesis. It occurs before DNA replication (S phase), ensuring the cell is ready for synthesis. Both assertion and reason are correct, with reason explaining the assertion. Answer: Both A and R are true, R is correct explanation.

8. Match the following:
Column I: 1. G1 phase 2. S phase 3. G2 phase 4. G0 phase
Column II: A. DNA replication B. Cell growth C. Quiescent stage D. Protein synthesis
Options:
A. 1-B, 2-A, 3-D, 4-C
B. 1-A, 2-B, 3-C, 4-D
C. 1-C, 2-D, 3-B, 4-A
D. 1-D, 2-C, 3-A, 4-B

Explanation: Correct matching: G1 – cell growth (B), S – DNA replication (A), G2 – protein synthesis (D), G0 – quiescent stage (C). Answer: 1-B, 2-A, 3-D, 4-C.

9. Fill in the blank: The phase between successive mitoses is called __________.
Options:
A. Interphase
B. Mitosis
C. Cytokinesis
D. S phase

Explanation: The phase between successive mitoses is interphase, consisting of G1, S, and G2 phases. During interphase, cells grow, replicate DNA, and prepare for division. Answer: Interphase.

10. Choose the correct statements:
1. G1 phase is for growth.
2. S phase is for DNA replication.
3. G2 phase is for protein synthesis.
4. G0 phase is inactive.
Options:
A. 1 and

Topic: Chromosomes and Cell Division
Subtopic: Chromosome Morphology

Keyword Definitions:

• Centromere: The primary constriction of a chromosome where sister chromatids are joined.

• Metacentric Chromosome: Chromosome with centromere in the middle, producing two equal arms.

• Acrocentric Chromosome: Chromosome with centromere near one end, producing one long arm and one short arm.

• Submetacentric Chromosome: Chromosome with centromere slightly off center, producing unequal arms.

• Telocentric Chromosome: Chromosome with centromere at the terminal end.

• Chromosome Arms: Sections of a chromosome on either side of the centromere.

• Sister Chromatids: Identical copies of a chromosome connected at the centromere.

• Karyotype: The complete set of chromosomes in a cell.

Lead Question - 2021

When the centromere is situated in the middle of two equal arms of chromosomes, the chromosome is referred as:
(1) Telocentric
(2) Sub-metacentric
(3) Acrocentric
(4) Metacentric

Explanation: Correct answer is (4) Metacentric. In metacentric chromosomes, the centromere lies in the middle, creating two arms of equal length. Acrocentric and submetacentric have unequal arms, and telocentric has the centromere at the end. Metacentric chromosomes are easiest to visualize during metaphase in karyotype analysis.

Guessed Questions:

1) Single Correct Answer: A chromosome with centromere at one end is called:
(1) Metacentric
(2) Acrocentric
(3) Telocentric
(4) Sub-metacentric

Explanation: Correct answer is (3) Telocentric. Telocentric chromosomes have centromeres at the terminal end, resulting in only one visible arm, unlike metacentric or acrocentric chromosomes.

2) Single Correct Answer: Chromosome with slightly off-center centromere is:
(1) Telocentric
(2) Sub-metacentric
(3) Metacentric
(4) Acrocentric

Explanation: Correct answer is (2) Sub-metacentric. Its centromere is near the center but not exactly in the middle, producing one arm slightly longer than the other, unlike perfectly equal metacentric chromosomes.

3) Single Correct Answer: Chromosome with centromere near the tip is:
(1) Acrocentric
(2) Metacentric
(3) Sub-metacentric
(4) Telocentric

Explanation: Correct answer is (1) Acrocentric. The centromere is close to one end, creating one long and one short arm. Commonly found in human chromosomes 13, 14, 15, 21, and 22.

4) Single Correct Answer: During karyotyping, equal-arm chromosomes are called:
(1) Metacentric
(2) Acrocentric
(3) Sub-metacentric
(4) Telocentric

Explanation: Correct answer is (1) Metacentric. They have a centrally located centromere and symmetrical arms, making them easy to identify in metaphase spreads.

5) Assertion-Reason:
A: Metacentric chromosomes have equal arms.
R: Centromere is in the middle of the chromosome.
(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: Correct answer is (1). The arms are equal because the centromere is centrally positioned, making the chromosome metacentric. The reason directly explains the assertion.

6) Single Correct Answer: The region joining sister chromatids is:
(1) Chromatid
(2) Centromere
(3) Kinetochore
(4) Telomere

Explanation: Correct answer is (2) Centromere. It holds sister chromatids together until anaphase, ensuring proper segregation during cell division.

7) Matching Type: Match chromosome types with centromere position:
List-I List-II
(a) Metacentric    (i) Near end
(b) Acrocentric    (ii) Middle
(c) Sub-metacentric    (iii) Slightly off-center
(d) Telocentric    (iv) Terminal

Explanation: Correct answer: (a) ii, (b) i, (c) iii, (d) iv. Each chromosome type is defined by the centromere location, which determines arm length and symmetry.

8) Single Correct Answer: Chromosome with arms of unequal length is:
(1) Metacentric
(2) Acrocentric
(3) Telocentric
(4) None

Explanation: Correct answer is (2) Acrocentric. The centromere is closer to one end, producing one long arm and one short arm.

9) Fill in the blank: Chromosomes with centromere at the center are called ______.
(1) Acrocentric
(2) Metacentric
(3) Sub-metacentric
(4) Telocentric

Explanation: Correct answer is (2) Metacentric. Central centromere placement results in two equal arms, characteristic of metacentric chromosomes.

10) Choose the correct statements:
(a) Metacentric chromosomes have equal arms.
(b) Sub-metacentric chromosomes have one arm longer.
(c) Telocentric chromosomes have centromere in the middle.
(d) Acrocentric chromosomes have centromere near one end.
Options:
(1) a, b, d
(2) a, c, d
(3) b, c, d
(4) a, b, c

Explanation: Correct answer is (1). Statements a, b, and d are correct. Statement c is incorrect; telocentric chromosomes have the centromere at the terminal end, not the middle.

Subtopic: Meiosis: Stages and Events

Keyword Definitions:

• Meiosis: A type of cell division that reduces the chromosome number by half to produce haploid gametes.

• Centromere: The region of a chromosome where sister chromatids are attached and spindle fibers connect.

• Metaphase II: Stage where chromosomes align at the equatorial plane in haploid cells.

• Anaphase II: Stage where centromeres divide, and sister chromatids move to opposite poles.

• Telophase II: Stage where nuclear membranes form around separated chromatids, forming haploid nuclei.

• Metaphase I: Stage where homologous chromosome pairs align at the equator in diploid cells.

• Sister Chromatids: Identical copies of a chromosome connected by a centromere.

• Reduction Division: First meiotic division reducing chromosome number by half, producing two haploid cells.

Lead Question - 2021

Which of the following stages of meiosis involves division of centromere?
(1) Metaphase II
(2) Anaphase II
(3) Telophase II
(4) Metaphase I

Explanation: The correct answer is (2) Anaphase II. During Anaphase II of meiosis, centromeres split, allowing sister chromatids to separate and move to opposite poles. This division is crucial for generating haploid gametes with single copies of each chromosome, unlike Anaphase I, where homologous chromosomes separate without centromere division.

Guessed Questions:

1) Single Correct Answer: During which stage of meiosis I do homologous chromosomes separate?
(1) Prophase I
(2) Metaphase I
(3) Anaphase I
(4) Telophase I

Explanation: The correct answer is (3) Anaphase I. In Anaphase I, homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached at centromeres, distinguishing this division from Anaphase II, which separates sister chromatids after centromere division.

2) Single Correct Answer: Sister chromatids separate during:
(1) Anaphase I
(2) Anaphase II
(3) Telophase I
(4) Metaphase I

Explanation: The correct answer is (2) Anaphase II. During this stage, centromeres divide, allowing sister chromatids to migrate toward opposite poles. This separation ensures each gamete receives one copy of each chromosome.

3) Single Correct Answer: Metaphase II is characterized by:
(1) Homologous chromosomes aligning
(2) Sister chromatids aligning at the equator
(3) Cytokinesis
(4) Crossing over

Explanation: The correct answer is (2). In Metaphase II, sister chromatids align along the equatorial plane of haploid cells. Spindle fibers attach to centromeres, preparing for their division in the next stage, Anaphase II.

4) Assertion (A): Centromere division occurs in Anaphase II.
Reason (R): Sister chromatids move to opposite poles.
(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). In Anaphase II, centromeres divide, allowing sister chromatids to separate and migrate to opposite poles. This ensures each haploid gamete receives one copy of each chromosome, completing the equational division.

5) Single Correct Answer: Telophase II results in:
(1) Diploid cells
(2) Haploid cells
(3) Polyploid cells
(4) Chromosome duplication

Explanation: The correct answer is (2) Haploid cells. Telophase II produces four haploid nuclei, each containing single chromatids. This stage follows centromere division in Anaphase II, completing meiosis and generating genetically unique gametes.

6) Single Correct Answer: Crossing over occurs during:
(1) Prophase I
(2) Metaphase I
(3) Anaphase I
(4) Telophase I

Explanation: The correct answer is (1) Prophase I. Homologous chromosomes exchange genetic material at chiasmata during this stage. This recombination increases genetic diversity before centromere division in Anaphase II and formation of haploid gametes.

7) Matching Type: Match stages of meiosis with events.
List-I    List-II
(a) Metaphase I    (i) Chromosomes align at equator
(b) Anaphase I    (ii) Homologous chromosomes separate
(c) Anaphase II    (iii) Sister chromatids separate
(d) Telophase II    (iv) Haploid nuclei form

Explanation: Correct answer: (a) i, (b) ii, (c) iii, (d) iv. Metaphase I aligns homologs, Anaphase I separates them, Anaphase II divides centromeres to separate sister chromatids, and Telophase II forms haploid nuclei, completing meiosis.

8) Single Correct Answer: Metaphase I differs from Metaphase II because:
(1) Homologous pairs align in Metaphase I
(2) Sister chromatids align in Metaphase II
(3) Both (1) and (2)
(4) Neither

Explanation: The correct answer is (3) Both (1) and (2). In Metaphase I, homologous chromosomes align at the equator, whereas in Metaphase II, sister chromatids align at the equator of haploid cells, preparing for centromere division in Anaphase II.

9) Fill in the blank: The stage in meiosis where centromeres divide is _______.
(1) Anaphase I
(2) Anaphase II
(3) Metaphase I
(4) Telophase II

Explanation: The correct answer is (2) Anaphase II. Sister chromatids are separated by centromere division, allowing them to migrate to opposite poles, essential for producing haploid gametes in meiosis.

10) Choose the correct statements:
(a) Centromere division occurs in Anaphase II.
(b) Homologous chromosomes separate in Anaphase I.
(c) Metaphase II aligns sister chromat

Topic: Gametogenesis
Subtopic: Haploid and Diploid Cells

Keyword Definitions:

• Haploid cells: Cells containing one set of chromosomes (n), produced by meiosis.

• Diploid cells: Cells containing two sets of chromosomes (2n), typical somatic cells.

• Primary oocyte: Diploid cell that undergoes meiosis I to form secondary oocyte.

• Secondary oocyte: Haploid cell formed after meiosis I of oogenesis, arrested in metaphase II.

• Spermatid: Haploid male gamete formed after meiosis II, matures into sperm.

• First polar body: Small haploid cell formed during oogenesis, usually degenerates.

• Ovum: Mature female gamete, haploid cell.

• Spermatogonia: Diploid male germ cells, divide mitotically to maintain germ line.

• Primary spermatocyte: Diploid cell that undergoes meiosis I in spermatogenesis.

• Secondary spermatocyte: Haploid cell after meiosis I, undergoes meiosis II to form spermatids.

• Second polar body: Haploid cell formed during oocyte meiosis II, usually degenerates.

Lead Question - 2020 (COVID Reexam)

Select the correct option of haploid cells from the following groups:

1. Primary oocyte, Secondary oocyte, Spermatid
2. Secondary spermatocyte, First polar body, Ovum
3. Spermatogonia, Primary spermatocyte, Spermatid
4. Primary spermatocyte, Secondary spermatocyte, Second polar body

Explanation: Haploid cells contain a single set of chromosomes (n). Secondary spermatocyte, first polar body, and ovum are haploid cells produced during meiosis in spermatogenesis and oogenesis. Primary oocytes and spermatocytes are diploid. Therefore, correct haploid group is secondary spermatocyte, first polar body, and ovum. Answer: Option 2.

1. Single correct answer MCQ:

Which of the following is haploid?
1. Primary oocyte
2. Secondary spermatocyte
3. Spermatogonia
4. Primary spermatocyte

Explanation: Haploid cells carry one set of chromosomes (n). Secondary spermatocytes are haploid, formed after meiosis I. Primary oocytes, spermatogonia, and primary spermatocytes are diploid (2n). Answer: Option 2.

2. Single correct answer MCQ:

First polar body is:
1. Diploid
2. Haploid
3. Tetraploid
4. Triploid

Explanation: The first polar body is formed during oogenesis after meiosis I. It contains a haploid set of chromosomes (n) and usually degenerates. Answer: Option 2.

3. Single correct answer MCQ:

Which of the following is diploid?
1. Ovum
2. Secondary spermatocyte
3. Primary spermatocyte
4. Spermatid

Explanation: Primary spermatocyte is diploid (2n) and undergoes meiosis I to produce haploid secondary spermatocytes. Ovum, secondary spermatocyte, and spermatid are haploid. Answer: Option 3.

4. Single correct answer MCQ:

During oogenesis, the ovum is:
1. Diploid
2. Haploid
3. Triploid
4. Tetraploid

Explanation: The ovum is the mature female gamete, produced after meiosis II, containing a haploid set of chromosomes (n). Answer: Option 2.

5. Single correct answer MCQ:

Spermatid originates from:
1. Spermatogonia
2. Primary spermatocyte
3. Secondary spermatocyte
4. Sertoli cells

Explanation: Spermatids are haploid cells produced from secondary spermatocytes after meiosis II. They further differentiate into spermatozoa. Answer: Option 3.

6. Single correct answer MCQ:

Which is not a haploid cell?
1. First polar body
2. Secondary oocyte
3. Primary spermatocyte
4. Ovum

Explanation: Primary spermatocyte is diploid (2n) and undergoes meiosis I to produce haploid secondary spermatocytes. First polar body, secondary oocyte, and ovum are haploid. Answer: Option 3.

7. Assertion-Reason MCQ:

Assertion (A): Spermatids are haploid cells.
Reason (R): Spermatids form after meiosis II.
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: Spermatids are haploid cells formed from secondary spermatocytes after meiosis II, making reason a correct explanation of the assertion. Answer: Option 1.

8. Matching Type MCQ:

Column I    Column II
(a) Primary spermatocyte    (i) Diploid
(b) Secondary spermatocyte    (ii) Haploid
(c) Spermatid    (iii) Haploid
(d) Ovum    (iv) Haploid

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

Explanation: Primary spermatocyte is diploid, secondary spermatocyte, spermatid, and ovum are haploid. Correct matching: (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv). Answer: Option 1.

9. Fill in the blanks:

________ are haploid cells resulting from meiosis II in males.
1. Spermatogonia
2. Spermatids
3. Primary spermatocytes
4. Sertoli cells

Explanation: Spermatids are haploid (n) cells formed from secondary spermatocytes after meiosis II. They eventually differentiate into mature spermatozoa. Answer: Option 2.

10. Choose correct statements:

(a) Secondary spermatocyte is haploid
(b) Primary oocyte is haploid
(c) Ovum is haploid
(d) Spermatogonia is haploid

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

Explanation: Secondary spermatocyte and ovum are haploid. Primary oocyte and spermatogonia are diploid. Therefore, correct statements are a and c only. Answer: Option 1.

Topic: Phases of Cell Cycle
Subtopic: Events in G1, S, G2, and M-phase

Keyword Definitions:

• G1 phase: First gap phase where cell grows and organelles duplicate.

• S phase: DNA synthesis phase where chromosomes are replicated.

• G2 phase: Second gap phase preparing for mitosis, involving cytoplasmic growth.

• M-phase: Mitotic phase including prophase, metaphase, anaphase, and telophase.

• Metaphase: Stage in mitosis where chromosomes align at the metaphase plate.

• Cell cycle: Sequence of events in a cell leading to its division and replication.

Lead Question - 2020 (COVID Reexam)

Match the following events that occur in their respective phases of cell cycle and select the correct option :

(a) G1 phase (i) Cell grows and organelle duplication
(b) S phase (ii) DNA replication and chromosome duplication
(c) G2 phase (iii) Cytoplasmic growth
(d) Metaphase in M-phase (iv) Alignment of chromosomes
Options:
1. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
2. (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
3. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
4. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation: In the cell cycle, G1 phase involves cell growth and organelle duplication, S phase is where DNA replication occurs, G2 phase involves cytoplasmic growth preparing for mitosis, and metaphase in M-phase is when chromosomes align at the metaphase plate. Correct answer is option 4: (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv). (50 words)

Guessed Question 1. Single Correct Answer MCQ: DNA synthesis occurs during :

1. G1 phase
2. S phase
3. G2 phase
4. M phase

Explanation: DNA replication takes place during the S phase of the cell cycle. G1 involves growth, G2 is cytoplasmic preparation for mitosis, and M phase is mitosis. Correct answer is option 2: S phase. Accurate DNA synthesis ensures each daughter cell receives identical genetic material. (50 words)

Guessed Question 2. Single Correct Answer MCQ: Cell growth and organelle duplication occur in :

1. G1 phase
2. S phase
3. G2 phase
4. M phase

Explanation: G1 phase is the first gap phase where the cell grows and organelles duplicate, preparing for DNA replication. S phase synthesizes DNA, G2 phase grows cytoplasm, and M phase is mitosis. Correct answer is option 1: G1 phase. Proper growth ensures functional daughter cells. (50 words)

Guessed Question 3. Single Correct Answer MCQ: Chromosome alignment at metaphase plate occurs in :

1. G1 phase
2. S phase
3. G2 phase
4. Metaphase

Explanation: During metaphase of M-phase, chromosomes align at the metaphase plate, ensuring equal segregation into daughter cells. G1 and G2 are preparatory phases, S is DNA replication. Correct answer is option 4: Metaphase. Proper alignment prevents aneuploidy and maintains genomic stability. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Cytoplasmic growth occurs in :

1. G1 phase
2. S phase
3. G2 phase
4. Metaphase

Explanation: Cytoplasmic growth occurs in G2 phase, preparing the cell for mitosis. G1 involves cell growth and organelle duplication, S phase is DNA replication, and metaphase is chromosome alignment. Correct answer is option 3: G2 phase. This ensures sufficient cellular components for two daughter cells. (50 words)

Guessed Question 5. Assertion-Reason MCQ:

Assertion (A): S phase is essential for genetic fidelity.
Reason (R): DNA replication occurs during S phase.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: DNA replication in S phase ensures accurate duplication of genetic material. Both assertion and reason are true, and the reason explains the assertion. Correct answer is option 1. This is critical for maintaining genetic fidelity and preventing mutations in daughter cells. (50 words)

Guessed Question 6. Matching Type:

Column I - Event
(a) DNA replication (i) S phase
(b) Chromosome alignment (ii) Metaphase
(c) Cytoplasmic growth (iii) G2 phase
(d) Cell growth and organelle duplication (iv) G1 phase
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: DNA replication occurs in S phase, chromosome alignment in metaphase, cytoplasmic growth in G2, and cell growth with organelle duplication in G1. Correct answer is option 1. Proper coordination ensures accurate division and genomic stability in daughter cells. (50 words)

Guessed Question 7. Fill in the blank:

The phase of the cell cycle immediately preceding mitosis is _______.

1. G1
2. S
3. G2
4. Metaphase

Explanation: G2 phase precedes mitosis, allowing cytoplasmic growth and final preparations. G1 is initial growth, S phase replicates DNA, and metaphase is part of M-phase. Correct answer is option 3: G2 phase. This ensures the cell is ready for accurate division. (50 words)

Guessed Question 8. Single Correct Answer MCQ: Which phase follows G1?

1. G0
2. S
3. G2
4. Metaphase

Explanation: S phase follows G1, where DNA is replicated to prepare for mitosis. G0 is a resting phase, G2 prepares cytoplasm, and metaphase is part of M-phase. Correct answer is option 2: S phase. Sequential progression maintains proper cell cycle and genetic stability. (50 words)

Guessed Question 9. Single Correct Answer MCQ: M-phase consists of :

1. G1, S, G2
2. Prophase, Metaphase, Anaphase, Telophase
3. DNA replication only
4. Cytoplasmic growth

Explanation: M-phase includes prophase, metaphase, anaphase, and telophase, completing nuclear division. G1, S, and G2 are interphase stages. Correct answer is option 2. Accurate execution of M-phase ensures equal chromosome segregation and formation of two genetically identical daughter cells. (50 words)

Guessed Question 10. Choose correct statements:

1. G1 involves cell growth
2. S phase is DNA replication
3. G2 prepares cytoplasm for mitosis
4. Metaphase aligns chromosomes
Options:
A. 1 and 2
B. 1, 2, and 3
C. 1, 2, 3, and 4
D. 2, 3, and 4

Explanation: All statements are correct: G1 is growth, S is DNA synthesis, G2 prepares cytoplasm, and metaphase aligns chromosomes. Correct answer is option C: 1, 2, 3, and 4. These coordinated events ensure proper cell division and genetic stability. (50 words)

Subtopic: Stages of Meiosis I

Keyword Definitions:

• Synapsis: Pairing of homologous chromosomes during prophase I of meiosis.

• Pachytene: Stage where crossing over occurs between homologous chromosomes.

• Zygotene: Stage when synapsis of homologous chromosomes begins.

• Diplotene: Stage when homologous chromosomes start separating but remain attached at chiasmata.

• Leptotene: Initial stage of prophase I with chromosomal condensation.

• Meiosis I: Reductional division producing two haploid cells from one diploid cell.

Lead Question - 2020 (COVID Reexam)

During Meiosis 1, in which stage synapsis takes place?

1. Pachytene
2. Zygotene
3. Diplotene
4. Leptotene

Explanation: Synapsis, the pairing of homologous chromosomes, occurs during zygotene of prophase I in meiosis. Pachytene follows zygotene and involves crossing over, diplotene shows chiasmata, and leptotene is the initial condensation stage. Correct answer is option 2: Zygotene. Proper synapsis ensures accurate genetic recombination. (50 words)

Guessed Question 1. Crossing over occurs during :

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene

Explanation: Crossing over, the exchange of genetic material between homologous chromosomes, occurs during pachytene stage of prophase I in meiosis. Leptotene is initial condensation, zygotene is synapsis, and diplotene shows chiasmata. Correct answer is option 3: Pachytene. This process increases genetic variation in gametes. (50 words)

Guessed Question 2. Chiasmata become visible in :

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene

Explanation: Chiasmata, points of contact where crossing over occurred, become visible in diplotene of prophase I. Leptotene is condensation, zygotene is synapsis, and pachytene is crossing over. Correct answer is option 4: Diplotene. Chiasmata ensure proper segregation of homologous chromosomes during meiosis I. (50 words)

Guessed Question 3. Initial chromosomal condensation occurs in :

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene

Explanation: Leptotene is the first stage of prophase I where chromosomes start condensing into visible threads. Zygotene involves synapsis, pachytene is crossing over, and diplotene shows chiasmata. Correct answer is option 1: Leptotene. Chromosomal condensation prepares homologous chromosomes for accurate pairing. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Homologous chromosomes separate in :

1. Meiosis I
2. Meiosis II
3. Mitosis
4. Interphase

Explanation: Homologous chromosomes separate during anaphase I of meiosis I, reducing the chromosome number by half. Meiosis II separates sister chromatids, mitosis separates sister chromatids without reduction, and interphase is preparatory. Correct answer is option 1: Meiosis I. Accurate separation is essential for producing haploid gametes. (50 words)

Guessed Question 5. Assertion-Reason:

Assertion (A): Synapsis occurs in zygotene.
Reason (R): Homologous chromosomes align for recombination.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: During zygotene, homologous chromosomes pair (synapsis) to facilitate recombination. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer is option 1. Synapsis ensures proper crossing over and genetic diversity in gametes. (50 words)

Guessed Question 6. Matching Type:

Column I - Stage
(a) Synapsis (i) Zygotene
(b) Crossing over (ii) Pachytene
(c) Chiasmata visible (iii) Diplotene
(d) Chromosome condensation (iv) Leptotene
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: Synapsis occurs in zygotene, crossing over in pachytene, chiasmata become visible in diplotene, and chromosome condensation begins in leptotene. Correct option is 1. This sequence ensures proper genetic recombination and chromosome segregation during meiosis I. (50 words)

Guessed Question 7. Fill in the blank:

The stage immediately following zygotene is _______.

1. Leptotene
2. Pachytene
3. Diplotene
4. Diakinesis

Explanation: Pachytene follows zygotene during prophase I of meiosis. It is the stage where crossing over occurs between homologous chromosomes. Leptotene precedes zygotene, diplotene follows pachytene, and diakinesis is the final stage of prophase I. Correct answer is option 2: Pachytene. (50 words)

Guessed Question 8. Single Correct Answer MCQ: Diakinesis is characterized by :

1. Synapsis initiation
2. Maximal chromosome condensation
3. Crossing over
4. Chromosome duplication

Explanation: Diakinesis is the final stage of prophase I where chromosomes achieve maximal condensation and prepare for metaphase I. Synapsis occurs in zygotene, crossing over in pachytene, and duplication in S phase. Correct answer is option 2: Maximal chromosome condensation. This ensures proper segregation during meiosis I. (50 words)

Guessed Question 9. During which stage are homologous chromosomes fully paired?

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene

Explanation: Homologous chromosomes are fully paired during pachytene, allowing crossing over at chiasmata. Zygotene initiates synapsis, leptotene is condensation, and diplotene shows partial separation. Correct answer is option 3: Pachytene. Full pairing is crucial for recombination and genetic diversity in gametes. (50 words)

Guessed Question 10. Choose correct statements:

1. Synapsis occurs in zygotene.
2. Crossing over occurs in pachytene.
3. Chiasmata visible in diplotene.
4. Leptotene is initial condensation.
Options:
A. 1 and 2
B. 1, 2, and 3
C. 1, 2, 3, and 4
D. 2, 3, and 4

Explanation: All four statements are correct: leptotene is initial condensation, zygotene shows synapsis, pachytene is crossing over, and diplotene shows chiasmata. Correct answer is option C: 1, 2, 3, and 4. This sequence ensures proper recombination and chromosome segregation during meiosis I. (50 words)

Topic: Mitotic Cell Cycle
Subtopic: Phases of Mitosis

Keyword Definitions:

• G1 Phase: First gap phase where cell grows and performs normal functions.

• S Phase: Synthesis phase where DNA is replicated to prepare for division.

• G2 Phase: Second gap phase for preparation and repair before mitosis.

• M Phase: Mitosis phase where nuclear division occurs, followed by cytokinesis.

• Mitotic Cycle: Series of phases that a cell undergoes to divide and produce two daughter cells.

• Cell Cycle Regulation: Mechanisms ensuring proper DNA replication and division.

Lead Question - 2020 (COVID Reexam)

In a mitotic cycle, the correct sequence of phases is :

1. S, G1, G2, M
2. G1, S, G2, M
3. M, G1, S, G2
4. G2, G1, S, M

Explanation: The mitotic cycle follows a precise order: G1 phase for growth, S phase for DNA replication, G2 phase for preparation, and M phase for mitosis. This sequence ensures accurate genetic material duplication and division. Therefore, the correct answer is option 2: G1, S, G2, M. (50 words)

Guessed Question 1. During which phase is DNA synthesized?

1. G1
2. S
3. G2
4. M

Explanation: DNA synthesis occurs during the S phase, ensuring each daughter cell receives an identical genome. G1 is growth, G2 is preparation for mitosis, and M phase involves chromosome segregation. Correct answer is option 2: S phase. Accurate replication prevents mutations and maintains genomic stability. (50 words)

Guessed Question 2. G1 phase is mainly for :

1. DNA replication
2. Cell growth
3. Nuclear division
4. Cytokinesis

Explanation: G1 is the first gap phase focused on cell growth, protein synthesis, and normal metabolic activities. DNA replication occurs in S phase, and nuclear division is in M phase. Cytokinesis happens post-mitosis. Correct answer is option 2: Cell growth. It prepares the cell for successful replication. (50 words)

Guessed Question 3. G2 phase function is :

1. Growth and repair
2. DNA synthesis
3. Chromosome condensation
4. Spindle formation

Explanation: G2 phase allows the cell to repair DNA replication errors, synthesize proteins for mitosis, and increase size. DNA synthesis occurs in S phase. Chromosome condensation and spindle formation occur in M phase. Correct answer is option 1: Growth and repair. This ensures accurate division. (50 words)

Guessed Question 4. M phase includes :

1. DNA replication
2. Nuclear division
3. Cell growth
4. Protein synthesis

Explanation: M phase encompasses mitosis, the nuclear division of chromosomes, and cytokinesis, the division of cytoplasm. DNA replication occurs in S phase, cell growth in G1, and protein synthesis throughout interphase. Correct answer is option 2: Nuclear division. Accurate division is essential for generating two genetically identical daughter cells. (50 words)

Guessed Question 5. Assertion-Reason Question:

Assertion (A): Mitosis is preceded by S phase.
Reason (R): DNA must be duplicated before nuclear division.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: DNA replication during S phase is necessary to ensure each daughter cell receives a complete set of chromosomes. Therefore, mitosis (M phase) is preceded by S phase. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer is option 1. (50 words)

Guessed Question 6. Matching Type Question:

Column I - Phase
(a) Growth before DNA synthesis (i) G1
(b) DNA replication (ii) S
(c) Preparation for mitosis (iii) G2
(d) Nuclear division (iv) M
Options:
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
3. (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
4. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Explanation: G1 is growth before DNA synthesis, S phase is DNA replication, G2 is preparation for mitosis, and M phase is nuclear division. Therefore, correct matching is option 1: (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv). This sequence ensures proper cell cycle progression. (50 words)

Guessed Question 7. Fill in the blank:

The phase immediately after S phase is _______.

1. G1
2. G2
3. M
4. Cytokinesis

Explanation: After DNA replication in S phase, the cell enters G2 phase to repair errors and prepare for mitosis. G1 precedes S phase, M follows G2, and cytokinesis occurs after mitosis. Correct answer is option 2: G2. Proper sequencing prevents mutations and ensures successful cell division. (50 words)

Guessed Question 8. Choose correct statements:

1. DNA replicates in S phase.
2. G1 phase is for growth.
3. Mitosis occurs in M phase.
4. G2 phase repairs errors.
Options:
A. 1 and 2
B. 1, 2, and 3
C. 1, 2, 3, and 4
D. 2 and 3

Explanation: All four statements are correct: DNA replication occurs in S phase, G1 is growth, M phase is mitosis, and G2 repairs errors. These coordinated events maintain genomic integrity and prepare the cell for division. Therefore, correct answer is option C: 1, 2, 3, and 4. (50 words)

Guessed Question 9. During which phase are proteins required for spindle formation synthesized?

1. G1
2. S
3. G2
4. M

Explanation: Proteins needed for spindle formation, including tubulin, are synthesized during G2 phase. This prepares the cell for M phase, where chromosomes segregate. G1 is growth, S replicates DNA, and M is division. Correct answer is option 3: G2 phase. Preparation ensures successful mitosis. (50 words)

Guessed Question 10. Assertion-Reason Question:

Assertion (A): Cell cycle checkpoints prevent abnormal division.
Reason (R): Checkpoints monitor DNA integrity and proper replication.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Checkpoints in G1, G2, and M phases ensure DNA is replicated correctly and damage is repaired before division. This prevents abnormal or incomplete mitosis. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer is option 1. (50 words)

Topic: Mitosis and Meiosis
Subtopic: Chromosome Segregation and Spindle Apparatus

Keyword Definitions:

• Spindle fibers: Microtubule structures that help segregate chromosomes during cell division.

• Kinetochore: Protein complex on the centromere of a chromosome where spindle fibers attach.

• Anaphase: Stage of mitosis when sister chromatids separate and move toward opposite poles.

• Telophase: Stage of mitosis where chromosomes decondense and nuclear envelope reforms.

• Prophase: Initial stage of mitosis where chromosomes condense and spindle begins to form.

• Metaphase: Stage of mitosis where chromosomes align at the cell equator, and spindle fibers attach to kinetochores.

Lead Question - 2020 (COVID Reexam)

Attachment of spindle fibers to kinetochores of chromosomes becomes evident in :

1. Anaphase
2. Telophase
3. Prophase
4. Metaphase

Explanation: Spindle fibers attach to kinetochores during metaphase, aligning chromosomes at the cell equator. This ensures proper segregation during anaphase. Attachment is not complete during prophase, and telophase or anaphase represents later stages. Therefore, the correct answer is option 4: Metaphase. Proper attachment is crucial for genetic stability. (50 words)

Guessed Question 1. During which stage do sister chromatids separate?

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Explanation: Sister chromatids separate and move toward opposite poles during anaphase. This segregation ensures that each daughter cell receives an identical set of chromosomes. Prophase and metaphase involve chromosome condensation and alignment, while telophase involves nuclear envelope reformation. Correct answer is option 3: Anaphase. (50 words)

Guessed Question 2. Chromosomes align at the equatorial plate in :

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Explanation: Chromosomes align at the metaphase plate during metaphase, with spindle fibers attached to kinetochores. This precise alignment is essential for equal segregation. Prophase involves condensation, anaphase separation, and telophase nuclear reformation. Correct answer is option 2: Metaphase. (50 words)

Guessed Question 3. Nuclear envelope disappears during :

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Explanation: The nuclear envelope breaks down in prophase to allow spindle fibers to interact with chromosomes. This is a key event in early mitosis. It is reformed during telophase. Metaphase and anaphase represent alignment and segregation stages. Correct answer is option 1: Prophase. (50 words)

Guessed Question 4. Telophase is characterized by :

1. Chromosome condensation
2. Spindle formation
3. Chromosome decondensation and nuclear reformation
4. Sister chromatid separation

Explanation: During telophase, chromosomes decondense and the nuclear envelope reforms around the separated chromatid sets, preparing for cytokinesis. Spindle disassembles, and cells return to interphase configuration. Condensation and separation occur in earlier stages. Correct answer is option 3: Chromosome decondensation and nuclear reformation. (50 words)

Guessed Question 5. Assertion-Reason Question:

Assertion (A): Kinetochores are essential for chromosome movement.
Reason (R): Spindle fibers attach to kinetochores to pull chromatids apart.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Kinetochores are protein structures where spindle fibers attach. This attachment enables chromatids to move toward opposite poles. Both assertion and reason are true, and the reason correctly explains the assertion. Therefore, correct answer is option 1: Both A and R true, R explains A. (50 words)

Guessed Question 6. Matching Type Question:

Column I - Stage
(a) Chromosome condensation (i) Prophase
(b) Alignment at equator (ii) Metaphase
(c) Chromatid separation (iii) Anaphase
(d) Nuclear envelope reformation (iv) Telophase
Options:
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
3. (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
4. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

Explanation: Chromosome condensation occurs in prophase. Alignment at the equatorial plate is metaphase. Chromatid separation occurs in anaphase. Nuclear envelope reforms in telophase. Correct matching is option 1: (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv). This sequence reflects the accurate mitotic stages. (50 words)

Guessed Question 7. Fill in the blank:

The _______ forms the mitotic spindle during cell division.

1. Nucleolus
2. Centrosome
3. Ribosome
4. Endoplasmic reticulum

Explanation: The centrosome organizes microtubules to form the mitotic spindle, enabling proper chromosome segregation. Nucleolus, ribosomes, and ER do not form spindles. Spindle fibers extend from centrosomes to kinetochores to pull chromatids apart. Correct answer is option 2: Centrosome. (50 words)

Guessed Question 8. Choose correct statements:

1. Spindle fibers attach to kinetochores in metaphase.
2. Sister chromatids separate in anaphase.
3. Nuclear envelope reforms in telophase.
4. Chromosome condensation occurs in telophase.
Options:
A. 1 and 2
B. 1, 2 and 3
C. 2 and 4
D. All 1, 2, 3, 4

Explanation: Correct statements: spindle fibers attach to kinetochores in metaphase, sister chromatids separate in anaphase, and nuclear envelope reforms in telophase. Chromosome condensation occurs in prophase, not telophase. Therefore, correct answer is option B: 1, 2, and 3. This highlights key mitotic events. (50 words)

Subtopic: Meiosis Phases and Events

Keyword Definitions:

• Zygotene – Stage of prophase I where homologous chromosomes start pairing (synapsis).

• Pachytene – Stage of prophase I where crossing over occurs between non-sister chromatids.

• Diplotene – Stage where homologous chromosomes start to separate but remain connected at chiasmata.

• Diakinesis – Final stage of prophase I marked by terminalization of chiasmata and chromosome condensation.

• Synapsis – Pairing of homologous chromosomes during meiosis.

• Chiasmata – X-shaped structure indicating the site of crossing over.

• Crossing over – Exchange of genetic material between non-sister chromatids of homologous chromosomes.

• Terminalization – Movement of chiasmata toward the ends of chromosomes.

• Homologous chromosomes – Chromosome pairs of similar length, gene position, and centromere location.

• Prophase I – First stage of meiosis I where recombination and synapsis occur.

• Meiosis – Type of cell division producing gametes with half the chromosome number.

Lead Question - 2020

Match the following with respect to meiosis:
(a) Zygotene – (i) Terminalization
(b) Pachytene – (ii) Chiasmata
(c) Diplotene – (iii) Crossing over
(d) Diakinesis – (iv) Synapsis
Select the correct option from the following:
(a) (b) (c) (d)
(1) (i) (ii) (iv) (iii)
(2) (ii) (iv) (iii) (i)
(3) (iii) (iv) (i) (ii)
(4) (iv) (iii) (ii) (i)

Explanation: In meiosis, Zygotene involves synapsis of homologous chromosomes (a-iv), Pachytene is the stage of crossing over (b-iii), Diplotene is characterized by visible chiasmata (c-ii), and Diakinesis shows terminalization of chiasmata (d-i). Therefore, the correct answer is (4) (iv) (iii) (ii) (i).

1. Single Correct Answer: Stage of prophase I where homologous chromosomes pair is:
(1) Pachytene
(2) Diplotene
(3) Zygotene
(4) Diakinesis

Explanation: Zygotene is the stage where synapsis occurs and homologous chromosomes begin pairing. This sets the stage for crossing over. Correct answer is (3) Zygotene.

2. Single Correct Answer: Stage where genetic recombination occurs is:
(1) Zygotene
(2) Pachytene
(3) Diplotene
(4) Diakinesis

Explanation: Pachytene is the phase of prophase I where crossing over occurs between non-sister chromatids, allowing genetic recombination. Correct answer is (2) Pachytene.

3. Single Correct Answer: Chiasmata become visible in which stage?
(1) Zygotene
(2) Pachytene
(3) Diplotene
(4) Diakinesis

Explanation: During Diplotene, homologous chromosomes begin to separate but remain connected at chiasmata, making the crossover points visible. Correct answer is (3) Diplotene.

4. Single Correct Answer: Terminalization of chiasmata occurs in:
(1) Zygotene
(2) Pachytene
(3) Diplotene
(4) Diakinesis

Explanation: Diakinesis is the final stage of prophase I where chiasmata move toward the ends of chromosomes, and chromosomes are fully condensed. Correct answer is (4) Diakinesis.

5. Assertion-Reason:
Assertion (A): Pachytene is the phase of crossing over.
Reason (R): Synapsis occurs during Pachytene.
(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: Pachytene is correctly the stage of crossing over, but synapsis occurs earlier in Zygotene, so reason is false. Correct answer is (3) A true, R false.

6. Single Correct Answer: Stage immediately following Zygotene is:
(1) Diakinesis
(2) Pachytene
(3) Diplotene
(4) Metaphase I

Explanation: After Zygotene, chromosomes are fully paired in Pachytene where crossing over occurs. Correct answer is (2) Pachytene.

7. Matching Type: Match meiosis stage with feature:
(a) Zygotene – i. Crossing over
(b) Pachytene – ii. Synapsis
(c) Diplotene – iii. Terminalization
(d) Diakinesis – iv. Chiasmata
Options:
(1) a-ii, b-i, c-iv, d-iii
(2) a-i, b-ii, c-iii, d-iv
(3) a-iv, b-iii, c-i, d-ii
(4) a-iii, b-iv, c-ii, d-i

Explanation: Correct matching: Zygotene – Synapsis, Pachytene – Crossing over, Diplotene – Chiasmata, Diakinesis – Terminalization. Correct answer is (1).

8. Fill in the blank: Stage where homologous chromosomes are fully synapsed is _______.
(1) Zygotene
(2) Pachytene
(3) Diplotene
(4) Diakinesis

Explanation: During Pachytene, homologous chromosomes are fully paired and crossing over occurs. Correct answer is (2) Pachytene.

9. Single Correct Answer: X-shaped structures indicating crossover are called:
(1) Synaptonemal complexes
(2) Chiasmata
(3) Centromeres
(4) Chromatids

Explanation: Chiasmata are visible X-shaped points where non-sister chromatids exchange genetic material. Correct answer is (2) Chiasmata.

10. Choose the correct statements:
(a) Synapsis occurs in Zygotene
(b) Crossing over occurs in Pachytene
(c) Chiasmata are visible in Diplotene
(d) Terminalization occurs in Diakinesis
Options:
(1) a, b, c, d

Subtopic: Interphase

Keyword Definitions:

• G1 Phase – First gap phase of interphase where cell grows and performs normal metabolic activities without DNA replication.

• S Phase – DNA synthesis or replication phase of interphase.

• G2 Phase – Second gap phase where cell prepares for mitosis with organelle replication and component reorganisation.

• M Phase – Mitotic phase where nuclear and cytoplasmic division occur.

• Interphase – Non-dividing phase of cell cycle consisting of G1, S, and G2 phases where cell prepares for mitosis.

• Cell Cycle – Sequence of events in cell life including growth, DNA replication, and division.

Lead Question - 2020

Identify the correct statement with regard to G1 phase (Gap 1) of interphase.
(1) Cell is metabolically active, grows but does not replicate its DNA.
(2) Nuclear Division takes place.
(3) DNA synthesis or replication takes place.
(4) Reorganisation of all cell components takes place.

Explanation: During G1 phase, the cell grows in size, synthesizes proteins and organelles, and is metabolically active, but DNA replication does not occur. Nuclear division happens in M phase, DNA synthesis occurs in S phase, and reorganisation of components mainly occurs in G2. Correct answer is (1).

1. Single Correct Answer: In which phase of interphase does DNA replication occur?
(1) G1 phase
(2) S phase
(3) G2 phase
(4) M phase

Explanation: DNA synthesis occurs specifically in the S phase of interphase. G1 is for growth, G2 for preparation for mitosis, M phase is division. Correct answer is (2) S phase.

2. Single Correct Answer: The main activity during G2 phase is:
(1) Cell growth and protein synthesis
(2) DNA replication
(3) Reorganisation of cell components for mitosis
(4) Nuclear division

Explanation: G2 phase prepares the cell for mitosis by reorganising organelles and proteins needed for division. DNA replication is completed in S phase, growth occurs in G1, and nuclear division occurs in M phase. Correct answer is (3).

3. Single Correct Answer: Which phase of the cell cycle includes G1, S, and G2 phases?
(1) M phase
(2) Interphase
(3) Cytokinesis
(4) Telophase

Explanation: Interphase consists of G1, S, and G2 phases where the cell grows, replicates DNA, and prepares for division. M phase and cytokinesis occur later. Correct answer is (2) Interphase.

4. Assertion-Reason:
Assertion (A): G1 phase is metabolically active but does not replicate DNA.
Reason (R): DNA replication occurs only in S phase.
(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: G1 phase is indeed metabolically active without DNA replication, which occurs in S phase. Therefore, both statements are correct, and R explains A. Correct answer is (1).

5. Single Correct Answer: Which activity is NOT characteristic of G1 phase?
(1) Protein synthesis
(2) Cell growth
(3) DNA replication
(4) Metabolic activity

Explanation: DNA replication occurs in S phase, not G1. G1 is focused on growth, protein synthesis, and metabolic activity. Correct answer is (3) DNA replication.

6. Single Correct Answer: Nuclear division occurs in which phase?
(1) G1 phase
(2) S phase
(3) G2 phase
(4) M phase

Explanation: Nuclear division occurs during the M phase of the cell cycle. G1, S, and G2 are interphase stages preparing for division. Correct answer is (4) M phase.

7. Matching Type: Match column I with column II:
a. G1 phase – i. DNA synthesis
b. S phase – ii. Cell growth
c. G2 phase – iii. Preparation for mitosis
d. M phase – iv. Nuclear division
(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: G1 phase is cell growth (a-ii), S phase is DNA synthesis (b-i), G2 phase is preparation for mitosis (c-iii), M phase is nuclear division (d-iv). Correct answer is (1).

8. Fill in the blank: DNA replication occurs during the ______ phase.
(1) G1
(2) S
(3) G2
(4) M

Explanation: DNA synthesis or replication occurs specifically in the S phase of interphase. G1 is for growth, G2 prepares for mitosis, and M is for division. Correct answer is (2) S.

9. Single Correct Answer: Which phase directly precedes mitosis?
(1) G1
(2) S
(3) G2
(4) Cytokinesis

Explanation: G2 phase is the final stage of interphase where the cell prepares for mitosis, ensuring all DNA is replicated and cell components are ready. Correct answer is (3) G2.

10. Choose the correct statements:
(a) G1 phase is for cell growth
(b) S phase is for DNA synthesis
(c) G2 phase is preparation for mitosis
(d) M phase is cytoplasmic division only
(1) a, b, c
(2) a, b, d
(3) b, c, d
(4) a, c, d

Explanation: G1 is growth (a), S is DNA replication (b), G2 is preparation for mitosis (c). M phase includes nuclear division and is not only cytoplasmic. Correct answer is (1) a, b, c.

Topic: Growth Phases

Subtopic: Logarithmic Phase

Keyword Definitions:

• Microbial growth – Increase in number or biomass of microorganisms over time.

• Lag phase – Initial adaptation phase with no significant cell division.

• Log phase – Exponential growth phase with maximum cell division and metabolic activity.

• Stationary phase – Growth slows as nutrient depletion and waste accumulation occur.

• Senescence – Aging phase where cells die or lose function.

• Dormancy – Metabolically inactive stage during unfavorable conditions.

Lead Question - 2020

The process of growth is maximum during:

(1) Senescence
(2) Dormancy
(3) Log phase
(4) Lag phase

Explanation: In the log phase, microorganisms divide at their maximum rate due to optimal nutrient availability and metabolic activity. Growth is exponential, leading to rapid increase in cell numbers. Other phases like lag, dormancy, or senescence have minimal or no growth. The correct answer is (3) Log phase.

1. During which phase do cells adjust to new medium without dividing?
(1) Lag phase
(2) Log phase
(3) Stationary phase
(4) Death phase

Explanation: In lag phase, cells metabolically adjust to the new environment by synthesizing enzymes and preparing for division. No significant increase in cell number occurs. The correct answer is (1) Lag phase.

2. Which phase shows nutrient limitation and accumulation of toxic metabolites?
(1) Log phase
(2) Stationary phase
(3) Lag phase
(4) Death phase

Explanation: In stationary phase, nutrient depletion and waste accumulation slow growth. The number of new cells equals dying cells, stabilizing population size. The correct answer is (2) Stationary phase.

3. Which phase follows stationary phase if nutrients are exhausted?
(1) Lag phase
(2) Death phase
(3) Log phase
(4) Dormancy

Explanation: Death phase occurs after stationary phase due to nutrient exhaustion and toxic metabolite buildup, leading to rapid cell death. The correct answer is (2) Death phase.

4. Assertion (A): Dormant cells show no growth.
Reason (R): Dormancy occurs under unfavorable conditions.
(1) Both A and R are true and R is correct explanation of A
(2) Both A and R are true but R is not correct explanation of A
(3) A is true but R is false
(4) A is false but R is true

Explanation: Dormant cells are metabolically inactive, ceasing growth. This occurs as a survival strategy under unfavorable conditions such as nutrient scarcity or stress. Both Assertion and Reason are true, and R correctly explains A. Correct answer is (1).

5. Which phase is targeted by antibiotics affecting cell wall synthesis?
(1) Lag phase
(2) Log phase
(3) Stationary phase
(4) Death phase

Explanation: Antibiotics like penicillin act during log phase when cells are actively dividing and synthesizing cell walls. Non-dividing cells in lag or stationary phases are less susceptible. Correct answer is (2) Log phase.

6. Maximum metabolic activity occurs during:
(1) Lag phase
(2) Log phase
(3) Stationary phase
(4) Senescence

Explanation: In log phase, cells are metabolically most active, synthesizing enzymes, proteins, and nucleic acids to support rapid division. Other phases show reduced metabolic activity. Correct answer is (2) Log phase.

7. Match the microbial phases with characteristics:
a. Lag phase – i. Rapid division
b. Log phase – ii. Adjustment period
c. Stationary phase – iii. Nutrient limitation
d. Death phase – iv. Cell death
(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: Correct matching: Lag phase involves adjustment (a-ii), log phase shows rapid division (b-i), stationary phase has nutrient limitation (c-iii), and death phase results in cell death (d-iv). Correct answer is (1).

8. Fill in the blank: The phase of bacterial growth with exponential increase in population is ______.
(1) Lag phase
(2) Log phase
(3) Stationary phase
(4) Death phase

Explanation: Log phase is characterized by exponential growth due to optimal nutrient conditions, leading to maximum cell division. Other phases have slow or no growth. Correct answer is (2) Log phase.

9. Single Correct Answer: Which phase is ideal for measuring generation time?
(1) Lag phase
(2) Log phase
(3) Stationary phase
(4) Death phase

Explanation: Generation time, the time for population to double, is best measured in log phase as cells divide at a constant exponential rate. Other phases do not show uniform growth. Correct answer is (2) Log phase.

10. Choose the correct statements:
(a) Senescence shows maximum growth
(b) Log phase is exponential growth
(c) Lag phase has active metabolic preparation
(d) Dormancy shows no division
(1) a, b only
(2) b, c, d only
(3) a, d only
(4) b, c only

Explanation: Log phase exhibits exponential growth (b), lag phase shows metabolic preparation (c), and dormancy shows no division (d). Senescence is not a growth phase. Correct statements are b, c, d. Correct answer is (2) b, c, d only.

Topic: Phases of Cell Cycle

Subtopic: Quiescent Stage (G0)

Keyword Definitions:

• Cell cycle – Sequence of events by which a cell grows, duplicates DNA, and divides.

• G1 phase – First growth phase with biosynthesis and preparation for DNA replication.

• S phase – DNA replication and synthesis of histones take place.

• G2 phase – Cell prepares for mitosis by synthesizing proteins and organelles.

• M phase – Includes karyokinesis (nuclear division) and cytokinesis (cytoplasmic division).

• Quiescent stage (G0) – Resting phase when cells leave the cycle after G1 and remain metabolically active but do not divide.

Lead Question - 2020

Some dividing cells exit the cell cycle and enter vegetative inactive stage. This is called quiescent stage (G0). This process occurs at the end of:

(1) S phase
(2) G2 phase
(3) M phase
(4) G1 phase

Explanation: Quiescent stage (G0) occurs when cells leave the active cycle after the G1 phase. They remain metabolically active but do not divide. Some cells like neurons stay permanently in G0. Hence, the process of entering G0 occurs after the G1 phase. The correct answer is (4) G1 phase.

1. Which phase of the cell cycle is longest?
(1) M phase
(2) G1 phase
(3) G2 phase
(4) S phase

Explanation: The G1 phase is typically the longest phase of the cell cycle, allowing growth and preparation for DNA synthesis. It accounts for major metabolic activities. Hence, the correct answer is (2) G1 phase.

2. DNA replication occurs during:
(1) G1 phase
(2) G2 phase
(3) S phase
(4) M phase

Explanation: DNA synthesis, along with histone production, takes place during the S phase of the cell cycle. This ensures each daughter cell receives a complete genome after division. The correct answer is (3) S phase.

3. Cyclins regulate progression of:
(1) Translation
(2) Transcription
(3) Cell cycle
(4) Replication fork

Explanation: Cyclins bind with cyclin-dependent kinases (CDKs) to regulate checkpoints and transitions between phases of the cell cycle, such as G1 to S and G2 to M. The correct answer is (3) Cell cycle.

4. G2-M transition is regulated by:
(1) p53
(2) MPF
(3) Cdk inhibitors
(4) Retinoblastoma protein

Explanation: Maturation-promoting factor (MPF), a complex of cyclin B and Cdk1, drives the cell from G2 into M phase. This ensures proper mitosis initiation. Hence, the answer is (2) MPF.

5. In which stage of mitosis do sister chromatids separate?
(1) Prophase
(2) Metaphase
(3) Anaphase
(4) Telophase

Explanation: During anaphase, centromeres split and sister chromatids move toward opposite poles. This ensures equal distribution of genetic material. The correct answer is (3) Anaphase.

6. Which is absent in animal cell division but present in plant cell division?
(1) Centrioles
(2) Spindle fibers
(3) Cell plate
(4) Asters

Explanation: Plant cells form a cell plate during cytokinesis due to the rigid cell wall, unlike animal cells which show cleavage furrow. Hence, the correct answer is (3) Cell plate.

7. Assertion (A): Neurons are permanently arrested in G0 phase.
Reason (R): They lack machinery for mitosis.
(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: Neurons enter G0 permanently and do not divide, as they lack the machinery required for cell cycle re-entry. Thus, both Assertion and Reason are true and R explains A correctly. The correct answer is (1).

8. Match the following cell types with their cell cycle behavior:
a. Hepatocytes – i. Divide frequently
b. Neurons – ii. Permanently G0
c. Skin cells – iii. Re-enter cell cycle when required
d. Stem cells – iv. Highly proliferative
(1) a-iii, b-ii, c-i, d-iv
(2) a-i, b-iii, c-iv, d-ii
(3) a-ii, b-iv, c-i, d-iii
(4) a-iv, b-i, c-ii, d-iii

Explanation: Hepatocytes enter G0 but can re-enter, neurons stay in permanent G0, skin cells divide frequently, and stem cells are highly proliferative. Correct matching is a-iii, b-ii, c-i, d-iv. The answer is (1).

9. Fill in the blank: The checkpoint that prevents damaged DNA from entering S phase is the ______.
(1) G2 checkpoint
(2) Spindle checkpoint
(3) G1 checkpoint
(4) Cytokinesis checkpoint

Explanation: The G1 checkpoint checks for DNA damage before replication. If damage exists, p53 halts the cycle or induces apoptosis. Thus, the correct answer is (3) G1 checkpoint.

10. Choose the correct statements:
(a) CDKs require cyclins to function.
(b) Centrosome duplication occurs in S phase.
(c) Cytokinesis occurs before telophase.
(d) G0 cells can never re-enter cell cycle.
(1) a, b only
(2) b, c only
(3) a, b only
(4) a, b, d only

Explanation: CDKs are functional only with cyclins, and centrosome duplication occurs during S phase. Cytokinesis begins after telophase, and G0 cells like hepatocytes may re-enter. Thus, correct statements are a and b. The correct answer is (3) a, b only.

Subtopic: Oogenesis and Fertilization

• Secondary oocyte: The haploid cell formed after the first meiotic division of the primary oocyte, which can undergo fertilization.

• Meiotic division: Cell division that reduces chromosome number by half, producing haploid gametes.

• Fertilization: Fusion of male and female gametes to form a zygote.

• Zygote: Diploid cell resulting from the fusion of sperm and ovum.

• Ovulation: Release of a mature oocyte from the ovary.

• Sperm-egg fusion: The process of sperm entering the ovum, triggering the completion of meiosis II.

• Oogenesis: Formation and maturation of female gametes (ova) in the ovary.

• Copulation: Sexual intercourse, which may lead to fertilization.

• Chromosome reduction: Halving of chromosome number during meiosis to maintain species-specific number in zygotes.

• Polar body: Small haploid cell produced during oogenesis that usually degenerates.

• Gamete maturation: Final changes in oocyte and sperm that enable successful fertilization.

Lead Question (2020): Meiotic division of the secondary oocyte is completed:
Options:
1. After zygote formation
2. At the time of fusion of a sperm with an ovum
3. Prior to ovulation
4. At the time of copulation

Explanation: Correct answer is 2. The secondary oocyte completes its second meiotic division only upon sperm entry. This ensures that meiosis II is triggered by fertilization, resulting in formation of the ovum and a second polar body, ultimately producing a diploid zygote after fusion of pronuclei.

1. Single Correct Answer MCQ:
During oogenesis, primary oocyte completes meiosis I to form:
Options:
a. Secondary oocyte
b. Zygote
c. Polar body only
d. Spermatid

Explanation: Correct answer is a. The primary oocyte undergoes meiosis I to produce a secondary oocyte and the first polar body. The secondary oocyte is haploid and remains arrested in metaphase II until fertilization occurs.

2. Single Correct Answer MCQ:
At which stage is the secondary oocyte arrested before ovulation?
Options:
a. Prophase I
b. Metaphase II
c. Telophase I
d. Anaphase II

Explanation: Correct answer is b. The secondary oocyte remains arrested at metaphase II of meiosis until fertilization. This ensures it is ready to complete meiosis II immediately upon sperm entry, forming the ovum and second polar body.

3. Single Correct Answer MCQ:
Which event triggers the completion of meiosis II in the secondary oocyte?
Options:
a. Ovulation
b. Copulation
c. Sperm penetration
d. Fertilized zygote cleavage

Explanation: Correct answer is c. Sperm penetration triggers meiosis II in the secondary oocyte. This leads to formation of the ovum and second polar body, ensuring that the resulting zygote has a diploid chromosome number.

4. Single Correct Answer MCQ:
Which cells are formed immediately after completion of meiosis II in the secondary oocyte?
Options:
a. Ovum and first polar body
b. Ovum and second polar body
c. Two secondary oocytes
d. Two primary oocytes