An antibiotic resistance gene of plasmid vector which get inactivated due to insertion of alien DNA, helps in the selection of

Options

A. Transformants
B. Recombinants
C. Non-Transformants
D. 2 & 3 both

Answer

To solve the question regarding the role of an antibiotic resistance gene in a plasmid vector that gets inactivated due to the insertion of alien DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Plasmid Vector**:
- A plasmid vector is a circular DNA molecule used in genetic engineering to clone foreign DNA. It often contains an antibiotic resistance gene that allows for the selection of successfully transformed cells.

2. **Identifying the Role of the Antibiotic Resistance Gene**:
- The antibiotic resistance gene provides the ability for bacteria to survive in the presence of a specific antibiotic (e.g., tetracycline). If the gene is functional, the bacteria can grow in an environment containing that antibiotic.

3. **Insertion of Alien DNA**:
- When foreign DNA is inserted into the plasmid vector at the site of the antibiotic resistance gene, it disrupts the gene's function. This means that the transformed bacteria will lose the ability to resist the antibiotic.

4. **Selection of Transformants**:
- In the selection process, transformed bacteria (those that have taken up the plasmid) can be distinguished from non-transformed bacteria. Since the antibiotic resistance gene is inactivated in the recombinant plasmid, these bacteria will not survive on media containing the antibiotic.

5. **Identifying Recombinants and Non-Recombinants**:
- The bacteria that have taken up the plasmid with the inactivated antibiotic resistance gene (recombinants) will not survive in the presence of the antibiotic. In contrast, non-recombinants (those that did not take up any plasmid) will also not survive, as they lack the plasmid's resistance.

6. **Conclusion**:
- Therefore, the inactivation of the antibiotic resistance gene allows for the selection of transformants (those that have taken up the plasmid) and helps in identifying recombinants (those that contain the foreign DNA). The correct answer to the question is **B (recombinants)**.

### Final Answer:
The antibiotic resistance gene of a plasmid vector, which gets inactivated due to the insertion of alien DNA, helps in the selection of **B (recombinants)**.