Which of the following is commonly used as a vector for introducing a DNA fragment in human lymphocytes ?

Options

A. (a) pBR 322
B. (b) `lambda` phage
C. (c) Ti plasmid
D. (d) Retrovirus

Answer

To determine which vector is commonly used for introducing a DNA fragment in human lymphocytes, we can analyze the provided options step by step:

1. **Understanding the Context**: The question is about vectors used in genetic engineering, specifically for human lymphocytes. Vectors are tools used to deliver genetic material into cells.

2. **Evaluating Option A - PBR322**:
- PBR322 is a plasmid vector primarily used in bacterial cells, not in human cells.
- **Conclusion**: This option is incorrect.

3. **Evaluating Option B - Lambda Phage**:
- Lambda phage can insert DNA fragments up to 23 kilobases (KB), but it is not suitable for human cells.
- **Conclusion**: This option is also incorrect.

4. **Evaluating Option C - Ti Plasmid**:
- Ti plasmid is used for transferring genes into plant cells, not human cells.
- **Conclusion**: This option is incorrect as well.

5. **Evaluating Option D - Retrovirus**:
- Retroviruses are commonly used in gene therapy for human cells. They have the ability to integrate their genetic material into the host genome, making them suitable for stable gene insertion.
- They also contain the enzyme reverse transcriptase, which allows RNA to be converted into DNA, facilitating the integration of genetic material.
- **Conclusion**: This option is correct.

6. **Final Answer**: The vector commonly used for introducing a DNA fragment in human lymphocytes is **Retrovirus**.