Part 3 — Meiosis I & II: Stages, Recombination & Significance (Q51–75)

Q51.

Which phase of meiosis I is the longest and most complex?
A. Anaphase I
B. Prophase I ✅
C. Metaphase I
D. Telophase I

Explanation:

A. Anaphase I: Chromosomes separate quickly.
B. Prophase I (Correct): Subdivided into leptotene, zygotene, pachytene, diplotene, diakinesis; involves pairing, recombination, synaptonemal complex.
C. Metaphase I: Alignment only.
D. Telophase I: Nuclear envelope reforms, short.

Q52.

During which substage of prophase I does crossing over occur?
A. Leptotene
B. Zygotene
C. Pachytene ✅
D. Diplotene

Explanation:

A. Leptotene: Chromosomes condense, no crossing over.
B. Zygotene: Synapsis begins.
C. Pachytene (Correct): Synapsis complete, recombination nodules mediate crossing over.
D. Diplotene: Chiasmata visible but crossing over already occurred.

Q53.

Chiasmata are first visible in which substage?
A. Leptotene
B. Pachytene
C. Diplotene ✅
D. Diakinesis

Explanation:

A. Leptotene: Chromosome condensation.
B. Pachytene: Crossing over occurs but chiasmata not yet visible.
C. Diplotene (Correct): Chiasmata appear as homologous chromosomes start repelling.
D. Diakinesis: Terminalization of chiasmata.

Q54.

The synaptonemal complex forms during:
A. Leptotene
B. Zygotene ✅
C. Pachytene
D. Diplotene

Explanation:

A. Leptotene: No SC yet.
B. Zygotene (Correct): SC forms to facilitate synapsis of homologues.
C. Pachytene: SC fully developed.
D. Diplotene: SC dissolves.

Q55.

Independent assortment of chromosomes occurs during:
A. Prophase I
B. Metaphase I ✅
C. Anaphase I
D. Metaphase II

Explanation:

A. Prophase I: Crossing over, not assortment.
B. Metaphase I (Correct): Random orientation of bivalents ensures independent segregation.
C. Anaphase I: Actual separation, but orientation decided earlier.
D. Metaphase II: Involves sister chromatids, not independent assortment of homologues.

Q56.

Reduction of chromosome number occurs during:
A. Anaphase I ✅
B. Metaphase I
C. Anaphase II
D. Telophase II

Explanation:

A. Anaphase I (Correct): Homologous chromosomes separate → reductional division.
B. Metaphase I: Chromosomes align, no reduction.
C. Anaphase II: Equational separation of chromatids.
D. Telophase II: Haploid nuclei form, no reduction occurs here.

Q57.

At the end of meiosis I, daughter cells are:
A. Diploid, with chromatids separated
B. Haploid, each with duplicated chromosomes ✅
C. Diploid, each with unreplicated chromosomes
D. Haploid, with single chromatids

Explanation:

**A. Diploid: incorrect, number reduced.
**B. Correct — each cell haploid, but chromosomes still have two chromatids.
**C. Diploid + unreplicated is false.
**D. Single chromatids only after meiosis II.

Q58.

Crossing over increases:
A. Mutation rate
B. Chromosome number
C. Genetic variability ✅
D. Ploidy stability

Explanation:

**A. Mutations are base changes, not recombination.
**B. Chromosome number unchanged.
**C. Correct — recombination creates new allele combinations.
**D. Ploidy changes only in reduction.

Q59.

Meiosis II is similar to mitosis because:
A. Homologous chromosomes pair
B. Sister chromatids separate ✅
C. Crossing over occurs
D. Ploidy is reduced

Explanation:

**A. Pairing: meiosis I.
**B. Correct — equational division like mitosis.
**C. Crossing over: prophase I only.
**D. Reduction occurs in meiosis I.

Q60.

In which stage of meiosis II do sister chromatids separate?
A. Prophase II
B. Metaphase II
C. Anaphase II ✅
D. Telophase II

Explanation:

A. Prophase II: Chromosomes condense again.
B. Metaphase II: Chromatids align.
C. Anaphase II (Correct): Centromeres split, chromatids move apart.
D. Telophase II: Nuclei reform.

Q61.

How many haploid gametes are produced from one diploid cell by meiosis?
A. 2
B. 3
C. 4 ✅
D. 8

Explanation:

**A. 2: produced in meiosis I, but meiosis II doubles this.
**B. 3: possible in female gametogenesis, but generally not.
C. 4 (Correct): Two meiotic divisions yield 4 haploid gametes.
**D. 8: requires another round of division.

Q62.

During which stage of meiosis do homologous chromosomes separate?
A. Anaphase I ✅
B. Metaphase I
C. Anaphase II
D. Telophase I

Explanation:

**A. Correct — homologous chromosomes segregate in anaphase I.
**B. Metaphase I: alignment.
**C. Anaphase II: chromatids separate.
**D. Telophase I: nuclear envelopes reappear.

Q63.

Synapsis is mediated by which structure?
A. Cohesin
B. Condensin
C. Synaptonemal complex ✅
D. Kinetochore

Explanation:

**A. Cohesin: holds chromatids, not homologues.
**B. Condensin: condenses chromosomes.
**C. Correct — proteinaceous ladder-like complex holding homologues together.
**D. Kinetochore: spindle attachment site.

Q64.

In diplotene, homologous chromosomes remain attached at:
A. Centromeres
B. Telomeres
C. Chiasmata ✅
D. Kinetochores

Explanation:

**A. Centromeres hold sister chromatids.
**B. Telomeres: chromosome ends, no attachment.
C. Chiasmata (Correct): Points of crossing over.
**D. Kinetochores: spindle attachment, not homologous pairing.

Q65.

Terminalization of chiasmata occurs in:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diakinesis ✅

Explanation:

A–C: Earlier substages.
D. Diakinesis (Correct): Final condensation, chiasmata migrate to ends.

Q66.

Which event ensures haploid chromosome number in gametes?
A. DNA replication in S phase
B. Homologous chromosome segregation in meiosis I ✅
C. Sister chromatid segregation in meiosis II
D. Crossing over

Explanation:

**A. Replication doubles DNA.
**B. Correct — reductional division in meiosis I ensures haploidy.
**C. Equational, not reductional.
**D. Crossing over = variation, not reduction.

Q67.

At the end of meiosis II, each daughter cell contains:
A. Diploid number of chromosomes
B. Haploid chromosomes with one chromatid each ✅
C. Haploid chromosomes with two chromatids each
D. Diploid chromosomes with chromatids

Explanation:

**A. Diploid: wrong, meiosis produces haploid.
**B. Correct — chromatids separate in meiosis II, yielding single-chromatid haploids.
**C. Two chromatids only before anaphase II.
**D. Diploid never restored until fertilization.

Q68.

The significance of crossing over is:
A. Maintaining chromosome number
B. Generating genetic diversity ✅
C. Preventing mutations
D. Ensuring spindle attachment

Explanation:

**A. Maintained by meiosis itself.
**B. Correct — recombination creates new allele combinations.
**C. Mutations unaffected.
**D. Spindle unrelated to crossing over.

Q69.

Which of the following happens in anaphase I but not in mitosis?
A. Centromeres split
B. Homologous chromosomes separate ✅
C. Chromosomes align at metaphase plate
D. Nuclear membrane breaks

Explanation:

**A. Centromere split = mitosis/anaphase II.
**B. Correct — homologues separate in meiosis I.
**C. Alignment occurs in both.
**D. Nuclear envelope breakdown occurs in both.

Q70.

The second meiotic division is called:
A. Reductional division
B. Equational division ✅
C. Mitotic division
D. Restitution division

Explanation:

**A. Reductional: meiosis I.
B. Equational (Correct): Chromatid separation without ploidy change.
**C. Mitosis differs.
**D. Restitution division refers to error leading to diploidy.

Q71.

In female meiosis, how many functional gametes are produced from one primary oocyte?
A. 4
B. 3
C. 2
D. 1 ✅

Explanation:

**A. 4 gametes = typical meiosis.
B/C. Incorrect for humans.
**D. Correct — oogenesis produces 1 ovum + 3 polar bodies.

Q72.

During meiosis I, chromosomes are present as:
A. Single chromatids
B. Duplicated homologous pairs (bivalents) ✅
C. Monads
D. Centrioles

Explanation:

**A. Not single yet.
**B. Correct — bivalents with 2 chromatids per chromosome, synapsed.
**C. Monads: single chromatids after meiosis II.
**D. Centrioles: spindle organizers.

Q73.

If a diploid cell has 20 chromosomes, how many chromosomes will each gamete have after meiosis?
A. 5
B. 10 ✅
C. 20
D. 40

Explanation:

**A. 5: not correct.
B. 10 (Correct): Haploid = half of diploid (20 → 10).
**C. 20: would be mitosis.
**D. 40: doubling, incorrect.

Q74.

Meiosis contributes to:
A. Asexual reproduction
B. Genetic stability and variation ✅
C. Wound healing
D. Somatic cell multiplication

Explanation:

**A. Asexual: mitosis.
**B. Correct — maintains chromosome number across generations + produces variation.
C/D. Somatic processes.

Q75.

In which meiotic substage do homologous chromosomes repel each other but remain attached at chiasmata?
A. Zygotene
B. Pachytene
C. Diplotene ✅
D. Diakinesis

Explanation:

**A. Zygotene: pairing begins.
**B. Pachytene: recombination.
C. Diplotene (Correct): Synaptonemal complex dissolves, homologues repulse but chiasmata hold them.
**D. Diakinesis: terminalization.

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Part 3 — Meiosis I & II: Stages, Recombination & Significance (Q51–75)