Zygotene of prophase-I is characterised by

Options

A. chromomeres
B. synaptonemal complex
C. crossing over
D. terminalisation of chiasmata.

Explanation

To answer the question regarding what characterizes the zygotene stage of prophase I in meiosis, follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: Zygotene is a stage within prophase I of meiosis, which is the process of cell division that leads to the formation of gametes.

2. **Identify Key Features of Zygotene**: During zygotene, the homologous chromosomes begin to pair up. This pairing is crucial for the next steps in meiosis.

3. **Define Homologous Chromosomes**: Homologous chromosomes are pairs of chromosomes that have the same structure and carry genes for the same traits, but may have different alleles.

4. **Formation of Bivalents**: As the homologous chromosomes align, they form structures known as bivalents. This is a key characteristic of the zygotene stage.

5. **Synaptonemal Complex**: The paired homologous chromosomes are held together by a protein structure known as the synaptonemal complex. This complex is essential for the process of recombination or crossing over, which occurs later in prophase I.

6. **Conclusion**: The defining characteristic of the zygotene stage is the presence of the synaptonemal complex, which facilitates the pairing of homologous chromosomes.

### Final Answer:
The zygotene of prophase I is characterized by the **synaptonemal complex**.