Name the stage of meiosis where crossing over occurs between non-sister chromatids of homologous chromosomes?

Options

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

Answer

To answer the question about the stage of meiosis where crossing over occurs between non-sister chromatids of homologous chromosomes, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Meiosis**: Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of gametes (sperm and egg cells). It consists of two main stages: Meiosis I and Meiosis II.

2. **Identify Chromosome Structure**: After the S phase of the cell cycle, each chromosome consists of two identical sister chromatids joined at a region called the centromere. Homologous chromosomes are pairs of chromosomes, one from each parent, that are similar in shape, size, and genetic content.

3. **Define Non-Sister Chromatids**: Non-sister chromatids refer to the chromatids of homologous chromosomes. For example, if you have two homologous chromosomes, each with two sister chromatids, the chromatids from different chromosomes are considered non-sister chromatids.

4. **Locate the Stage of Crossing Over**: Crossing over is the process where non-sister chromatids exchange genetic material. This occurs during a specific stage of Meiosis I.

5. **Identify the Specific Stage**: The stage of meiosis where crossing over occurs is called the **Pachytene stage**. This is part of Prophase I of Meiosis I, where homologous chromosomes pair up and exchange segments of genetic material.

6. **Conclusion**: Therefore, the correct answer to the question is the **Pachytene stage** of meiosis.

### Final Answer:
The stage of meiosis where crossing over occurs between non-sister chromatids of homologous chromosomes is the **Pachytene stage**.

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