Restriction endonuclease was isolated for the first time by W. Aber in 1962 in bacteria. Restriction endonucleases cut the DNA duplex at specific points therefore they are also called as molecular scissors or biological scissors. Three types of restriction endemicleases are Type 1. Type II and Type III but only Type II restriction endonucleases are used in recombinant DNA technology. Restriction endonuclease EcoR I recognises the base sequence GAATTC In DNA duplex and cut strands between G and A.
Which type of restriction endonucleases is used most in genetic engineering?

Options

A. Type I
B. Type II
C. Type III
D. Type IV

Explanation

To answer the question, "Which type of restriction endonucleases is used most in genetic engineering?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases, also known as restriction enzymes, are proteins that cut DNA at specific sequences. They were first isolated by W. Aber in 1962 from bacteria.

2. **Types of Restriction Endonucleases**:
- There are three main types of restriction endonucleases: Type I, Type II, and Type III.
- Each type has different characteristics and methods of action.

3. **Characteristics of Each Type**:
- **Type I Restriction Endonucleases**: These enzymes cut DNA at a site that is far from their recognition site (about 1000 base pairs away). They require ATP for their activity.
- **Type II Restriction Endonucleases**: These are the most commonly used in genetic engineering. They cut DNA at specific sites within or near their recognition sequences, which are often palindromic. They do not require ATP for their activity.
- **Type III Restriction Endonucleases**: These enzymes cut DNA about 24-26 base pairs away from their recognition site and also require ATP.

4. **Application in Genetic Engineering**:
- In genetic engineering, precise cuts in DNA are essential for cloning and manipulating genes. Type II restriction endonucleases are preferred because they provide specific and predictable cuts at defined locations.

5. **Conclusion**:
- Given the characteristics and applications of the different types, the type of restriction endonuclease most commonly used in genetic engineering is **Type II**.

### Final Answer:
**Type II restriction endonucleases are used most in genetic engineering.**

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