Prophase-I is divided into five phases based on

Options

A. Chromosome number
B. Time duration
C. Chromosome behaviour
D. Crossing over patterns

Answer

**Step-by-Step Solution:**

1. **Understanding Prophase I**: Prophase I is a crucial stage of meiosis, which is a type of cell division that reduces the chromosome number by half. It is significantly longer than other stages of meiosis.

2. **Subdivisions of Prophase I**: Prophase I is divided into five distinct sub-stages:
- **Leptotene**: Chromosomes begin to condense and become visible under a microscope.
- **Zygotene**: Homologous chromosomes start to pair up in a process called synapsis.
- **Pachytene**: Crossing over occurs between non-sister chromatids of homologous chromosomes, leading to genetic recombination.
- **Diplotene**: The synaptonemal complex dissolves, and structures called chiasmata (where crossing over occurred) become visible.
- **Diakinesis**: The chiasmata terminalize, and the chromosomes prepare for separation.

3. **Criteria for Division**: The division of Prophase I into these five phases is based on the behavior of chromosomes during these stages. Each phase exhibits distinct chromosomal behaviors, such as visibility, pairing, crossing over, and the formation and resolution of chiasmata.

4. **Conclusion**: Therefore, Prophase I is divided into five phases primarily based on the changing behavior of chromosomes throughout these stages.

5. **Correct Answer**: The correct answer to the question is that Prophase I is divided into five phases based on **chromosome behavior**.

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