Most important stage for the evolution of new species is

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:**
The question asks for the most important stage for the evolution of new species among the options provided: leptotin, zygotin, pachyten, and diplotin.

2. **Identifying the Context:**
All the options are substages of Prophase I in meiosis, which is a type of cell division that reduces the chromosome number from diploid to haploid.

3. **Explaining Meiosis:**
Meiosis consists of two main stages: Meiosis I and Meiosis II. Prophase I is further divided into five substages: leptotin, zygotin, pachyten, diplotin, and diakinesis.

4. **Analyzing Each Substage:**
- **Leptotin:** Chromosomes start to become visible, but no crossing over occurs.
- **Zygotin:** Homologous chromosomes pair up (synapsis) but crossing over has not yet happened.
- **Pachyten:** This is where crossing over occurs, leading to genetic recombination.
- **Diplotin:** Crossing over is completed, and the chromosomes start to separate.

5. **Identifying the Key Stage:**
The pachyten stage is crucial because it is during this stage that crossing over takes place. This process leads to genetic variation, which is essential for the evolution of new species.

6. **Conclusion:**
Therefore, the most important stage for the evolution of new species is the **pachyten** stage.

**Final Answer:** Pachyten

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