During meiosis, replication of chromosomes occurs in

Options

A. S-phase
B. S-phase and zygotene
C. S-phase and leptotene
D. All the above

Answer

**Step-by-Step Text Solution:**

1. **Understanding Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of four haploid cells from one diploid cell. It consists of two consecutive divisions: meiosis I and meiosis II.

2. **Chromosome Replication**: Before any type of cell division, including meiosis, the genetic material (DNA) must be replicated. This ensures that each daughter cell receives the correct amount of genetic information.

3. **S Phase**: The replication of chromosomes occurs during the S phase (Synthesis phase) of the cell cycle. This phase is part of interphase, which precedes meiosis. During the S phase, each chromosome is duplicated, resulting in two identical sister chromatids for each chromosome.

4. **Chromosome Structure Before and After Replication**:
- Before replication, each chromosome is referred to as a "monad" (single chromatid).
- After replication, each chromosome consists of two sister chromatids, referred to as a "dyad".

5. **Conclusion**: Therefore, during meiosis, the replication of chromosomes occurs specifically in the S phase. The other options (S phase and zygotene, S phase and leptotene, and all of the above) are incorrect because the actual replication happens solely in the S phase.

**Final Answer**: The correct answer is option 1: S phase.

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