When does synapsis occur in meiosis?

Options

A. zygotene
B. Ieptotene
C. diplotene
D. pachytene

Answer

**Step-by-Step Solution:**

1. **Understanding Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half and is essential for sexual reproduction. It consists of two consecutive divisions: meiosis I and meiosis II.

2. **Phases of Meiosis**: Meiosis I is divided into several stages, including prophase I, metaphase I, anaphase I, and telophase I. Prophase I is further divided into five substages: leptotene, zygotene, pachytene, diplotene, and diakinesis.

3. **Identifying the Stages**: The question asks about synapsis, which is the pairing of homologous chromosomes. The relevant stages to consider are:
- **Leptotene**: Chromosomes start to condense and become visible.
- **Zygotene**: Homologous chromosomes begin to pair up.
- **Pachytene**: The paired chromosomes undergo crossing over.
- **Diplotene**: The homologous chromosomes start to separate.
- **Diakinesis**: The chromosomes condense further and prepare for separation.

4. **Locating Synapsis**: Synapsis specifically occurs during the **zygotene stage** of prophase I. During this stage, homologous chromosomes align closely together, forming pairs known as bivalents or tetrads.

5. **Formation of Synaptonemal Complex**: During zygotene, the homologous chromosomes are held together by a protein structure called the synaptonemal complex, which facilitates the pairing process.

6. **Conclusion**: Therefore, synapsis occurs in the **zygotene stage** of meiosis I.

**Final Answer**: Synapsis occurs during the zygotene stage of meiosis I.

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