Which of the following enzyme is used to join DNA fragments :

Options

A. Ligase
B. terminase
C. DNA polymerase
D. Endonuclease

Explanation

To determine which enzyme is used to join DNA fragments, we can analyze the options provided:

1. **Understanding the question**: The question asks for the enzyme that facilitates the joining of DNA fragments. This is a common process in genetic engineering, particularly in gene cloning.

2. **Analyzing the options**:
- **A. Ligase**: This enzyme is known for its role in joining DNA fragments by forming phosphodiester bonds between them. It is essential in processes like DNA replication and repair.
- **B. Terminase**: This enzyme is involved in the packaging of viral DNA into capsids, not in joining DNA fragments.
- **C. DNA Polymerase**: This enzyme synthesizes new DNA strands by adding nucleotides to a growing chain but does not join existing DNA fragments.
- **D. Endonuclease**: This enzyme cuts DNA at specific sites, which is the opposite of joining DNA fragments.

3. **Conclusion**: Based on the analysis, the enzyme that is specifically used to join DNA fragments is **DNA ligase**.

4. **Final Answer**: The correct option is **A. Ligase**.