Genetic engineering is possible because

Options

A. the phenomenon of transduction in bacteria is well understood
B. restriction endonuclease purified from bacteria can be used in vitro
C. we can cut DNA at specific sites by endonuclease like DNAase I
D. we can see DNA by electron microscope

Answer

### Step-by-Step Solution:

1. **Understanding Genetic Engineering**:
- Genetic engineering involves manipulating the genetic material (DNA) of an organism to alter its characteristics. This can include adding, removing, or altering DNA sequences.

2. **Role of Restriction Endonucleases**:
- Restriction endonucleases are enzymes that cut DNA at specific sequences. They are crucial for genetic engineering because they allow scientists to cut DNA from one organism and insert it into another.

3. **Source of Restriction Endonucleases**:
- These enzymes are purified from bacteria. They are naturally occurring in bacteria and serve as a defense mechanism against viral DNA.

4. **In Vitro Application**:
- The restriction endonucleases can be used in vitro, meaning they can function outside of the bacterial cells in a laboratory setting. This allows for the manipulation of DNA in controlled environments.

5. **Specificity of Cuts**:
- Each restriction endonuclease recognizes specific palindromic sequences in the DNA. For example, EcoR1 recognizes the sequence GAATTC and cuts between G and A, creating sticky ends that can be easily ligated with other DNA fragments.

6. **Importance of Sticky Ends**:
- The sticky ends produced by the cuts made by restriction endonucleases facilitate the joining of different DNA fragments. This is essential for the process of genetic engineering, where DNA from different sources is combined.

7. **Conclusion**:
- Genetic engineering is possible primarily because restriction endonucleases, which are purified from bacteria, can be used in vitro to cut DNA at specific sites, allowing for the manipulation and recombination of genetic material.

### Final Answer:
Genetic engineering is possible because restriction endonucleases purified from bacteria can be used in vitro to cut DNA at specific sites.

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