The process of crossing over is assisted by which of the following enzymes?

Options

A. Endonuclease
B. Polymerase
C. Ligase
D. Both a and c

Explanation

To solve the question regarding which enzymes assist in the process of crossing over, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Crossing Over**:
- Crossing over, also known as recombination, occurs during the pachytene stage of meiosis. It involves the exchange of genetic material between non-sister chromatids of homologous chromosomes.

2. **Identifying the Enzymatic Process**:
- The process of crossing over is enzyme-mediated, meaning that specific enzymes facilitate the steps involved in this process.

3. **Breaking of Chromatid Segments**:
- The first step in crossing over is the breaking of chromatid segments. This step is facilitated by the enzyme **endonuclease**. Endonucleases are enzymes that cut the phosphodiester bond within a nucleic acid chain.

4. **Reunion or Annealing of Chromatid Segments**:
- The second step involves the reunion or annealing of the broken chromatid segments. This step is mediated by the enzyme **ligase**. Ligases are enzymes that join two nucleic acid strands together by forming a phosphodiester bond.

5. **Conclusion**:
- Since both endonuclease and ligase are involved in the process of crossing over, the correct answer to the question is option **D**, which states "both A and C".

### Final Answer:
The process of crossing over is assisted by both endonuclease and ligase (Option D: both A and C).

---