Assertion: Ti-plasmids & retrovirus are used as vectors in gene transfer process
Reason :They have the natural art of delivering genes in their eukaryotic hosts

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion
B. It both Assertion & Reason are True but Reason is not a correct explanation of the Assetion
C. If Assertion is True but the Reason is False
D. If both Assertion & Reason are false

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that Ti-plasmids and retroviruses are used as vectors in the gene transfer process.
- **Explanation**: Ti-plasmids (Tumor Inducing plasmids) are derived from the bacterium Agrobacterium tumefaciens, which can transfer its DNA into plant cells, making them effective vectors for gene transfer in plants. Retroviruses, on the other hand, are viruses that can integrate their genetic material into the host's DNA, making them suitable vectors for gene transfer in animal cells.

2. **Understanding the Reason**: The reason states that Ti-plasmids and retroviruses have a natural ability to deliver genes into their eukaryotic hosts.
- **Explanation**: Ti-plasmids naturally transfer genes to plant cells when Agrobacterium infects them, leading to tumor formation and incorporation of the plasmid DNA into the plant genome. Retroviruses have a similar mechanism, where they can insert their RNA into the host's genome, allowing for stable gene expression.

3. **Evaluating the Relationship**: We need to determine if the reason provided is a correct explanation of the assertion.
- **Explanation**: Since both Ti-plasmids and retroviruses possess the natural ability to deliver genes into their respective eukaryotic hosts (plants for Ti-plasmids and animals for retroviruses), the reason effectively explains why they are used as vectors in gene transfer.

4. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion.
- **Final Answer**: Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation for the assertion.