The enzymes which are commonly used in genetic engineering are

Options

A. restriction endonuclease
B. ligase
C. gyrase and polymerase.
D. helicase

Answer

### Step-by-Step Solution:

1. **Understanding Genetic Engineering**: Genetic engineering involves the manipulation of genes, where genes from one organism are transferred to another organism. This process can change the phenotype of the recipient organism.

2. **Identifying the Enzymes Used**: The enzymes commonly used in genetic engineering include:
- **Restriction Endonucleases**: These enzymes cut DNA at specific sites. They are crucial for isolating the gene of interest from the DNA.
- **Ligase**: After cutting the DNA, ligase is used to join the DNA fragments together. It helps in binding the cut ends of DNA strands.
- **Gyrase**: This enzyme helps in maintaining the structure of DNA during replication.
- **Polymerase**: It adds nucleotides to form new DNA strands during DNA replication.
- **Helicase**: This enzyme unwinds the DNA double helix by breaking the hydrogen bonds between the nitrogenous bases.

3. **Main Enzymes for Genetic Engineering**: The primary enzymes used specifically for the purpose of genetic engineering are:
- **Restriction Endonucleases**: For cutting DNA.
- **Ligase**: For joining DNA fragments.

### Final Answer:
The enzymes which are commonly used in genetic engineering are **Restriction Endonucleases** and **Ligase**.

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