Which cannot be used for direct gene transfer

Options

A. Biolistics (gene gun)
B. Microinjection
C. Electroporation
D. Agrobacterium tumefacians

Answer

To solve the question "Which cannot be used for direct gene transfer?", we need to analyze the options provided and understand the mechanisms of gene transfer involved.

### Step-by-Step Solution:

1. **Understand Direct Gene Transfer**: Direct gene transfer refers to methods where genetic material is introduced into a cell without the use of a vector. This means that the DNA is delivered directly into the target cells.

2. **Analyze Each Option**:
- **Biolistics**: This method, also known as the gene gun method, involves shooting DNA-coated particles into cells. It is a direct method of gene transfer.
- **Gene Gun**: Similar to biolistics, it uses high-velocity microprojectiles to deliver DNA into cells, making it a direct method.
- **Microinjection**: This technique involves using a fine needle to inject DNA directly into the nucleus of a cell. It is a direct method of gene transfer.
- **Electroporation**: This method uses an electrical field to increase the permeability of the cell membrane, allowing DNA to enter the cell directly. It is also a direct method.
- **Agrobacterium tumefaciens**: This is a bacterium that naturally transfers DNA to plant cells. It acts as a vector for gene transfer, meaning it is not a direct method since it relies on a biological vector to deliver the genetic material.

3. **Conclusion**: Among the options, Agrobacterium tumefaciens cannot be used for direct gene transfer because it functions as a vector for transferring genetic material into plant cells. Therefore, the correct answer is **Agrobacterium tumefaciens**.

### Final Answer:
The option that cannot be used for direct gene transfer is **Agrobacterium tumefaciens**.