Crossing over requires an enzyme

Options

A. Recombinase
B. Ligase
C. Polymerase
D. Endonuclease

Answer

### Step-by-Step Solution:

1. **Understanding Crossing Over**:
- Crossing over is a process that occurs during meiosis where segments of DNA are exchanged between non-sister chromatids of homologous chromosomes. This leads to genetic variation in the offspring.

2. **Identifying the Enzyme Required**:
- To facilitate this exchange of DNA segments, specific enzymes are involved. The question asks which enzyme is necessary for crossing over.

3. **Evaluating the Options**:
- The options provided are:
- **Recombinase**
- **Ligase**
- **Polymerase**
- **Endonuclease**

4. **Analyzing Each Option**:
- **Recombinase**: This enzyme catalyzes the exchange of DNA segments between homologous chromosomes during crossing over.
- **Ligase**: This enzyme is responsible for joining DNA fragments together, particularly during DNA replication, but does not facilitate crossing over.
- **Polymerase**: This enzyme synthesizes new DNA strands by adding nucleotides during DNA replication, not involved in crossing over.
- **Endonuclease**: This enzyme cuts the polynucleotide chain at specific sites but does not catalyze the exchange of DNA segments.

5. **Conclusion**:
- Based on the analysis, the correct enzyme required for crossing over is **Recombinase**. It specifically catalyzes the exchange of homologous regions between paired maternal and paternal chromosomes.

### Final Answer:
The enzyme required for crossing over is **Recombinase**.

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