Zygotene is characterized by
Pairing of homologous chromosomes
Appearance of synaptonemal complex
Formation of bivalents
Formation of chiasmata

Options

A. (A), (B) & (D) Only
B. (B), C & (D) only
C. All except C
D. All except (D)

Answer

To solve the question regarding the characteristics of zygotene, we will analyze each option provided:

1. **Pairing of homologous chromosomes**:
- During zygotene, homologous chromosomes begin to pair up. This process is essential for the later stages of meiosis, as it allows for genetic recombination.
- **Hint**: Remember that zygotene is the stage where homologous chromosomes start to align closely.

2. **Appearance of synaptonemal complex**:
- The synaptonemal complex is a protein structure that forms between homologous chromosomes during zygotene. It facilitates the pairing of homologous chromosomes and is crucial for crossing over.
- **Hint**: Think of the synaptonemal complex as a "zipper" that holds homologous chromosomes together.

3. **Formation of bivalents**:
- Bivalents are formed when homologous chromosomes are fully paired and synapsed. This is a key feature of zygotene, as it indicates that the chromosomes are ready for genetic exchange.
- **Hint**: Bivalents consist of two homologous chromosomes that are paired together.

4. **Formation of chiasmata**:
- Chiasmata are the points where homologous chromosomes exchange genetic material during crossing over. However, this process occurs later in prophase I of meiosis, not during zygotene.
- **Hint**: Chiasmata are formed after zygotene, during the next stage of prophase I.

Based on this analysis, we can conclude that the characteristics of zygotene include:
- Pairing of homologous chromosomes
- Appearance of synaptonemal complex
- Formation of bivalents

However, the formation of chiasmata does not occur during zygotene, but rather in the later stages of prophase I.

**Final Answer**: Zygotene is characterized by the pairing of homologous chromosomes, the appearance of the synaptonemal complex, and the formation of bivalents, but not by the formation of chiasmata.