Question

If a foreign DNA is inserted in tetracycline resistant gene, the recombinant plasmid

• A. Will lose ampicillin resistance
• B. Will lose tetracycline resistance
• C. Cloning would become easier
• D. Ampicillin resistance will become stronger

Hint:

Recombinant selection uses insertional inactivation of resistance genes.

Answer 1

The Correct Option is B

Step 1: Double antibiotic resistance marker in pBR322.
pBR322 has resistance genes for both ampicillin and tetracycline. If a foreign gene is inserted into one of these, that resistance is lost.
Step 2: Insertion in tetracycline resistance gene.
If foreign DNA is inserted into the tetracycline resistance gene, the bacteria carrying recombinant plasmid will not be resistant to tetracycline.
Step 3: Conclusion.
Thus, insertion leads to loss of tetracycline resistance.