Enzymes help in crossing over

Options

A. Endonuclease and ligase
B. Restriction endonuclease and ligase
C. Endonuclease and exonuclease
D. Polymerase and endonuclase

Answer

**Step-by-Step Solution:**

1. **Understanding Crossing Over**: Crossing over is a process that occurs during meiosis, specifically in the pachytene stage of prophase I. It involves the exchange of genetic material between homologous chromosomes, which leads to genetic variation.

2. **Identifying the Role of Enzymes**: During crossing over, two main events occur:
- **Breaking of Chromatids**: This is where the chromatids of homologous chromosomes break at specific points.
- **Reunion of Chromatids**: After the breaking, the chromatids then recombine or reunite, leading to the exchange of genetic material.

3. **Enzymes Involved in Crossing Over**:
- **Endonuclease**: This enzyme is responsible for the breaking of the chromatid segments. It cuts the DNA at specific sites, allowing for the exchange of genetic material.
- **Ligase**: After the segments have been broken and exchanged, ligase is responsible for sealing the nicks in the DNA, thus reuniting the chromatids.

4. **Conclusion**: Based on the roles of these enzymes, we can conclude that the correct answer to the question "Enzymes help in crossing over" is **endonuclease and ligase**.

5. **Final Answer**: The correct option is **endonuclease and ligase**.

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