Insertion of a foreign DNA at BamHI site in an E.coli cloning vector pBR322 results in the loss of antibiotic resistance towards:

Question

Accepted Answer

C. 1. **Understanding pBR322** — This plasmid vector carries two antibiotic resistance genes: one for **ampicillin** and one for **tetracycline**, along with unique restriction sites within these genes.

2. **Where BamHI cuts** — The **BamHI** restriction site lies within the **tetracycline resistance gene** of pBR322.

3. **Effect of inserting foreign DNA** — Given that the foreign DNA is ligated at the BamHI site, it disrupts the tetracycline resistance gene through **insertional inactivation**.

$$
	ext{Foreign DNA at BamHI site} ightarrow tet^{R} 	ext{ gene disrupted}
$$

So, the recombinant plasmid loses its tetracycline resistance, while ampicillin resistance remains unaffected.

Hence, the answer is **Option C**: Tetracycline.