Bivalent chromosomes clearly appears as tetrad in

Options

A. Zygotene
B. Pachytene
C. Diplotene
D. Diakinesis

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks in which stage of meiosis the bivalent chromosomes clearly appear as tetrads.

2. **Identifying the Stages of Prophase I**: Prophase I of meiosis is divided into five stages: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.

3. **Analyzing Each Stage**:
- **Leptotene**: In this stage, chromosomes begin to condense and become visible, but they are not yet paired.
- **Zygotene**: Here, homologous chromosomes begin to pair up, a process known as synapsis. The synapto-nemal complex forms, but the bivalents (paired homologous chromosomes) are not yet clearly visible.
- **Pachytene**: This is the stage where crossing over occurs, and the bivalent chromosomes are fully formed and clearly visible as tetrads. This is the key stage for the question.
- **Diplotene**: In this stage, the homologous chromosomes start to separate but remain connected at points called chiasmata.
- **Diakinesis**: The chromosomes condense further, and the chiasmata terminalize, preparing for metaphase.

4. **Conclusion**: The bivalent chromosomes clearly appear as tetrads in the Pachytene stage of Prophase I during meiosis.

5. **Final Answer**: The correct answer is Pachytene.

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