Diplotene stage of prophase-I is characterised by

Options

A. dissolution of synaptonemal complex
B. separation of synapsed homologous chromosomes except at the site of crossovers
C. formation of X-shaped structures called chiasmata
D. all of these

Answer

### Step-by-Step Solution:

1. **Understanding the Diplotene Stage**: The diplotene stage is part of prophase I in meiosis, which is crucial for sexual reproduction. This stage follows the pachytene stage and is the second last stage of prophase I.

2. **Dissolution of Synaptonemal Complex**: During the diplotene stage, the synaptonemal complex, which holds homologous chromosomes together, begins to dissolve. This is a key characteristic of this stage.

3. **Separation of Synapsed Homologous Chromosomes**: As the synaptonemal complex dissolves, the homologous chromosomes start to separate from each other. However, this separation does not occur at the points where crossing over (exchange of genetic material) has taken place.

4. **Formation of Chiasmata**: The points where crossing over occurred form X-shaped structures known as chiasmata. These structures are crucial for ensuring proper segregation of chromosomes during meiosis.

5. **Conclusion**: The diplotene stage is characterized by:
- Dissolution of the synaptonemal complex.
- Separation of synapsed homologous chromosomes except at crossover points.
- Formation of X-shaped structures called chiasmata.

6. **Final Answer**: Therefore, the correct answer to the question is "all of these."