In which phase of cell division process of synapsis occurs ?

Question

Accepted Answer

The process of synapsis occurs during the zygotene phase of cell division, specifically during meiosis. Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in the production of gametes or spores. It consists of two consecutive divisions: meiosis I and meiosis II. Synapsis is a crucial event that occurs during prophase I of meiosis I.

1. **Explanation for Option 2 (Zygotene):**
   - During the zygotene stage of prophase I, homologous chromosomes begin to pair up in a process known as synapsis. This pairing is facilitated by the formation of a protein structure called the synaptonemal complex, which holds the homologous chromosomes together. Synapsis is essential for the subsequent processes of crossing over and genetic recombination, which increase genetic diversity. Therefore, the zygotene stage is correctly identified as the phase where synapsis occurs.

2. **Explanation for why other options are incorrect:**
   - **Option 1 (Pachytene):** In the pachytene stage, synapsis has already been completed. This phase is characterized by the occurrence of crossing over, where homologous chromosomes exchange genetic material. While pachytene is crucial for genetic recombination, it is not the phase where synapsis begins.
   - **Option 3 (Diplotene):** During the diplotene stage, the synaptonemal complex dissolves, and homologous chromosomes begin to separate, although they remain connected at chiasmata where crossing over has occurred. Synapsis is not initiated in this phase; rather, it is a stage where the effects of synapsis and crossing over become evident.
   - **Option 4 (Diakinesis):** Diakinesis is the final stage of prophase I, where chromosomes condense further, and the nuclear envelope breaks down. The homologous chromosomes are still connected at chiasmata, but synapsis is not occurring at this stage. Instead, the cell is preparing to transition into metaphase I.

In summary, synapsis specifically occurs during the zygotene stage of prophase I in meiosis, making Option 2 the correct answer. The other stages, while important in the process of meiosis, do not involve the initiation of synapsis.