Crossing over takes place between which chromatids and in which stage of the cell cycle ?

Options

A. Non-sister chromatids of non-homologous chromosomes at Zygotene stage of prophase I
B. Non-sister chromatids of homologous chromosomes at Pachytene stage of prophase I
C. Non-sister chromatids of homologous chromosomes at Zygotene stage of prophase I
D. Non-sister chromatids of non-homologous chromosomes at Pachytene stage of prophase I

Answer

**Step-by-Step Solution:**

1. **Understanding Crossing Over**:
- Crossing over is a process that occurs during meiosis, where homologous chromosomes exchange segments of genetic material. This process increases genetic diversity in the resulting gametes.

2. **Identifying Chromatids Involved**:
- The chromatids involved in crossing over are the non-sister chromatids of homologous chromosomes. Homologous chromosomes are pairs of chromosomes that have the same genes but may have different alleles.

3. **Determining the Stage of Meiosis**:
- Crossing over occurs during prophase I of meiosis. Prophase I is divided into several stages, and the specific stage where crossing over takes place is called the pachytene stage.

4. **Conclusion**:
- Therefore, crossing over takes place between the non-sister chromatids of homologous chromosomes during the pachytene stage of prophase I in meiosis.

**Final Answer**: Crossing over takes place between non-sister chromatids of homologous chromosomes during the pachytene stage of prophase I.

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