Crossing is an enzyme-mediated process. The enzyme is -

Options

A. DNA ligase
B. Recomblnase
C. RNAase
D. DNAase

Answer

### Step-by-Step Solution:

1. **Understanding the Process of Crossing Over**:
- Crossing over is a crucial process that occurs during meiosis, specifically in prophase I. It involves the exchange of genetic material between homologous chromosomes.

2. **Identifying the Stage of Meiosis**:
- The specific stage where crossing over occurs is called the pachytene stage of prophase I. During this stage, homologous chromosomes pair up closely.

3. **Role of Enzymes in Crossing Over**:
- The process of crossing over is facilitated by enzymes. These enzymes help in the physical exchange of segments between the chromatids of homologous chromosomes.

4. **Naming the Enzyme**:
- The enzyme responsible for mediating the crossing over process is known as **recombinase**. This enzyme plays a vital role in the formation of recombinant chromosomes, which are essential for genetic diversity.

5. **Conclusion**:
- Therefore, the enzyme that mediates the crossing over process during meiosis is **recombinase**.

### Final Answer:
The enzyme that mediates crossing over is **recombinase**.

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