Restriction endonuclease is used in

Options

A. Tissue culture
B. Genetic engineering
C. Cell fractionation
D. Regeneration of tissues

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases, also known as restriction enzymes, are proteins that cut DNA at specific sequences.
- They recognize specific short sequences of nucleotides, known as restriction sites, and cleave the DNA at these sites.

2. **Identifying the Correct Application**:
- The question asks for the application of restriction endonucleases. Among the options provided, the correct application is in genetic engineering.
- Other options like tissue culture, cell fractionation, or regeneration of tissues do not directly involve the use of restriction endonucleases.

3. **Mechanism of Action**:
- Restriction enzymes cut DNA at specific palindromic sequences. A palindromic sequence reads the same forwards and backwards on complementary strands.
- For example, the sequence GAATTC is palindromic because it reads the same in both directions.

4. **Example of a Restriction Enzyme**:
- EcoRI is a commonly used restriction enzyme that recognizes the palindromic sequence GAATTC and cuts between G and A.
- This cleavage allows for the manipulation of DNA, enabling the insertion of new genes or the modification of existing ones.

5. **Application in Genetic Engineering**:
- After cutting the DNA, the resulting fragments can be used to insert new genes or create recombinant DNA.
- This is a fundamental technique in genetic engineering, allowing scientists to modify organisms for various purposes, such as producing insulin or developing genetically modified crops.

### Final Answer:
Restriction endonucleases are primarily used in **genetic engineering**.

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