NEET Biology Cell Cycle and Cell Division MCQs Set 23

Answer: (c) anaphase II

Explanation:
1. Centromeres split only when sister chromatids separate.
2. That happens in anaphase II of meiosis.

Teacher's Note:
1. Anaphase I separates homologues instead.
2. Same fact appears in several forms in exams.

Answer: (d) Interphase

Explanation:
1. Interphase looks quiet under the microscope.
2. In fact the cell is highly active, growing and replicating DNA.

Teacher's Note:
1. Interphase is the most active metabolic phase.
2. It takes more than 95 percent of the cycle in many cells.

Answer: (c) paired meiotic chromosomes

Explanation:
1. It is a protein scaffold between synapsed homologues.
2. It forms only in meiotic prophase I.

Teacher's Note:
1. No synapsis, no synaptonemal complex.
2. Mitosis lacks homologue pairing.

Answer: (d) Anaphase

Explanation:
1. Chromosomes keep the number 2n through G2, prophase and metaphase.
2. Splitting of centromeres in anaphase doubles the number of chromosomes to 4n.

Teacher's Note:
1. The number doubles temporarily only in anaphase and telophase.
2. Do not confuse it with DNA content, which doubles in S phase.

Answer: (c) anaphase

Explanation:
1. Centromeres split lengthwise at the onset of anaphase.
2. This lets sister chromatids move to opposite poles.

Teacher's Note:
1. Anaphase starts with the centromere split.
2. The event is simultaneous for all chromosomes.

Answer: (b) anaphase II

Explanation:
1. Chromosomes of anaphase II are the separated sister chromatids.
2. Those of anaphase I, metaphase I and metaphase II still have two chromatids.

Teacher's Note:
1. Single-chromatid chromosomes appear after centromere split.
2. In meiosis this is only from anaphase II.

Answer: (c) 8 and 8

Explanation:
1. 8 bivalents mean n = 8 and 2n = 16.
2. Meiosis I halves the number to 8 per cell.
3. Meiosis II separates chromatids but does not change the number, so it remains 8.

Teacher's Note:
1. Reduction happens in meiosis I.
2. Meiosis II is like mitosis in terms of number.

Answer: (d) Exchange of genetic material occurs only in meiosis

Explanation:
1. Cytokinesis and spindle formation occur in both divisions, and mitosis also has DNA replication.
2. Crossing over (exchange between non-sister chromatids) is a feature of meiotic prophase I.

Teacher's Note:
1. Eliminate options with the word only one by one.
2. Recombination is the hallmark of meiosis.

Answer: (a) nucleus divides twice but DNA replicates only once

Explanation:
1. Meiosis I and II are two nuclear divisions.
2. The S phase occurs only once, before meiosis I.

Teacher's Note:
1. No S phase in interkinesis.
2. This is why the number of chromosomes ends up halved.

Answer: (b) genetically different

Explanation:
1. Crossing over exchanges segments between non-sister chromatids.
2. The two chromatids of a chromosome therefore carry different alleles.

Teacher's Note:
1. Sister chromatids are identical only if no crossing over occurred.
2. This is the source of variation.

Answer: (c) diplotene

Explanation:
1. The synaptonemal complex dissolves in diplotene.
2. Homologues start separating and chiasmata, the sites of crossing over, become visible as X-shapes.

Teacher's Note:
1. Chiasmata are visible from diplotene.
2. They move to the ends in diakinesis.

Answer: (d) telophase

Explanation:
1. Telophase reverses the changes of prophase.
2. The nuclear envelope and nucleolus reform and chromosomes decondense.

Teacher's Note:
1. Telophase is the reverse of prophase.
2. Cytokinesis usually follows.

Answer: (a) prophase

Explanation:
1. Chromatin condenses and centrosomes move apart forming asters in prophase.
2. This is the first stage of karyokinesis.

Teacher's Note:
1. Prophase is the build-up phase.
2. Asters are absent in higher plants.

Answer: (d) all of the above

Explanation:
1. Nuclear envelopes reform around the two sets of chromosomes.
2. Nucleoli reappear and the spindle and asters disassemble.

Teacher's Note:
1. Telophase mirrors prophase.
2. All three events happen together.

Answer: (b) synapsis

Explanation:
1. Pairing of homologues takes place in zygotene.
2. The paired structure is a bivalent.

Teacher's Note:
1. Synapsis forms bivalents.
2. Disjunction is the separation later in anaphase I.

Answer: (c) leptotene, zygotene, pachytene, diplotene, diakinesis

Explanation:
1. The order follows chromosome behaviour: thin threads, pairing, crossing over, chiasmata, terminalisation.
2. That gives leptotene, zygotene, pachytene, diplotene, diakinesis.

Teacher's Note:
1. Use the mnemonic LZPDD for the order.
2. Prophase I is the longest phase of meiosis.

Answer: (b) prophase, metaphase, anaphase and telophase

Explanation:
1. The M-phase is the actual division, covering the four stages of karyokinesis.
2. G1, S and G2 belong to interphase.

Teacher's Note:
1. Interphase is separate from M-phase.
2. Cytokinesis usually completes M-phase.

Answer: (a) G1 phase

Explanation:
1. G1 comes before the S phase.
2. G2 is the post-DNA-synthesis phase.

Teacher's Note:
1. Pre means before S.
2. G2 is also called the pre-mitotic phase.

Answer: (a) Meiosis I

Explanation:
1. Meiosis I reduces the chromosome number from 2n to n, so it is a reduction division.
2. It is therefore called heterotypic division, while meiosis II is homotypic.

Teacher's Note:
1. Heterotypic means reductional.
2. Meiosis II and mitosis are equational.

Answer: (a) mitosis and meiosis I

Explanation:
1. Both divisions are preceded by an S phase (before mitosis and before meiosis I).
2. There is no replication before meiosis II.

Teacher's Note:
1. Interkinesis has no S phase.
2. Replication is once per cycle.

Answer: (c) pachytene

Explanation:
1. Bivalents become shorter and thicker in pachytene.
2. Each bivalent shows four chromatids, a tetrad.

Teacher's Note:
1. Pachytene means thick thread.
2. Crossing over occurs in this stage.