Zygotene of prophase-I is characterised by the formation of

Options

A. Chromomeres
B. Synaptonemal complex
C. Crossing over
D. Terminalisation of chiasmata

Answer

### Step-by-Step Solution:

1. **Understanding Zygotene**: Zygotene is the second stage of prophase I in meiosis. It follows leptotene and precedes pachytene. During this stage, homologous chromosomes begin to pair up.

2. **Formation of Synaptonemal Complex**: One of the key features of zygotene is the formation of the synaptonemal complex. This structure is essential for the pairing of homologous chromosomes and consists of proteinaceous filaments that connect the homologs.

3. **Exclusion of Other Options**:
- **Ideomere Formation**: While ideomeres (or chromomeres) are present, they are not a defining characteristic of zygotene.
- **Crossing Over**: This process occurs during the pachytene stage, not zygotene. Therefore, it cannot be characterized by zygotene.
- **Terminalization of Chiasmata**: This occurs later in prophase I, specifically during diplotene, and is not a feature of zygotene.

4. **Conclusion**: Based on the characteristics of zygotene, the correct answer is the formation of the synaptonemal complex.

### Final Answer:
Zygotene of prophase I is characterized by the formation of the **synaptonemal complex**.

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