The correct answer is Tetracycline.

pBR322 is a widely used cloning vector that carries two antibiotic‑resistance genes:

• The ampR gene, which provides resistance to ampicillin, is located upstream of the multiple‑cloning site and is not part of the BamHI restriction site.

• The tetR gene, which provides resistance to tetracycline, is situated within the BamHI site of the vector.

When a foreign DNA fragment is inserted at the BamHI site, the BamHI recognition sequence (GGATCC) is cut and the ends are joined to the inserted fragment. This ligation disrupts the continuity of the tetracycline‑resistance gene, rendering it non‑functional.

Because the ampicillin‑resistance gene remains intact, the recombinant plasmid still confers ampicillin resistance, but the loss of a functional tetR gene means the host cells can no longer survive on tetracycline‑containing media.

Therefore, insertion at the BamHI site specifically eliminates resistance to tetracycline.