Which of the following vector is used extensively for genetic engineering in animals?

Options

A. E.coli
B. Ti plasmid
C. Bacillus thuriengenensis
D. Retrovirus (disarmed)

Answer

To determine which vector is used extensively for genetic engineering in animals, we can analyze the options provided:

1. **E. coli**: This is a bacterium commonly used in genetic engineering, but it is primarily used for cloning and manipulating DNA in bacteria, not directly in animals.

2. **Ti plasmid**: This is a vector derived from the bacterium Agrobacterium tumefaciens, which is primarily used for genetic engineering in plants, not animals.

3. **Bacillus thuringiensis**: This is a bacterium known for its insecticidal properties and is used in pest control, but it is not a vector for genetic engineering in animals.

4. **Retrovirus**: Retroviruses are RNA viruses that can integrate their genetic material into the host genome. They are extensively used as vectors for gene therapy and genetic engineering in animals, particularly in mammalian cells.

Based on this analysis, the vector that is used extensively for genetic engineering in animals is **Retrovirus**.

### Step-by-Step Solution:
1. **Identify the options**: Look at the given vectors: E. coli, Ti plasmid, Bacillus thuringiensis, and Retrovirus.
2. **Analyze each option**:
- E. coli: Used mainly for bacterial genetic engineering.
- Ti plasmid: Used for plants, not animals.
- Bacillus thuringiensis: Used for pest control, not as a vector in animals.
- Retrovirus: Known for integrating into the host genome, used in gene therapy for animals.
3. **Select the correct vector**: Based on the analysis, Retrovirus is the most suitable vector for genetic engineering in animals.

### Final Answer: Retrovirus