Chiasmata or X-shaped structures become visible during

Options

A. Diplotene stage
B. Zygotene stage
C. Pachytene stage
D. Leptotene stage

Answer

To determine when chiasmata or X-shaped structures become visible during meiosis, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half and involves two rounds of division: meiosis I and meiosis II. The first division (meiosis I) is crucial for genetic recombination.

2. **Identify Prophase I Stages**: Prophase I of meiosis is divided into several stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis. Each stage has distinct characteristics.

3. **Leptotene Stage**: In this initial stage, chromosomes begin to condense and become visible as thin threads. However, chiasmata are not yet visible.

4. **Zygotene Stage**: Chromosomes continue to condense, and homologous chromosomes begin to pair up (synapsis). Still, chiasmata are not visible.

5. **Pachytene Stage**: The paired homologous chromosomes (tetrads) become more distinct. This is the stage where crossing over occurs, but chiasmata are not yet prominent.

6. **Diplotene Stage**: This is the critical stage where chiasmata become visible. The homologous chromosomes begin to separate slightly, and the points of crossing over appear as X-shaped structures, which are the chiasmata.

7. **Diakinesis Stage**: In this final stage of Prophase I, the chromosomes condense further, and the chiasmata are still visible, but this is where the crossing over has completed.

8. **Conclusion**: Chiasmata are prominently visible during the Diplotene stage of Prophase I in meiosis.

### Final Answer:
Chiasmata or X-shaped structures become visible during the **Diplotene stage** of Prophase I in meiosis.

---