Question

A foreign DNA is inserted within the Pst I site of the $Am{p}^R$ gene in vector pBR322. Host bacteria were transformed with the engineered plasmid. Choose incorrect statement(s) from the following:
A. Recombinants will lose ampicillin resistance.
B. Recombinants will grow on a medium containing ampicillin but not on that containing tetracycline.
C. Non-recombinant transformed cells will grow on a medium containing both the antibiotics.
D. Recombinants will grow on a medium containing tetracycline but not on that containing ampicillin.

• A. b and c
• B. only b
• C. only c
• D. c and d

Answer 1

The correct answer is option D: Recombinants will grow on a medium containing tetracycline but not on that containing ampicillin.

pBR322:

1. The DNA molecule pBR322 was the first artificial cloning vector constructed by Bolivar and Rodriguez.
2. It has two antibiotic resistance genes: Ampicillin resistance gene and tetracycline resistance gene.
3. The restriction site for Pst-I lies within the ampicillin resistance gene.
4. The insertion of a foreign gene at this site will inactivate the ampicillin resistance gene, which is referred to as insertional inactivation.
5. As a result, when the recombinant DNA is inserted into the host cell, it will confer resistance against only tetracycline and not ampicillin.
6. Hence, recombinants will grow on an agar medium containing tetracycline only but not on that containing ampicillin.