Question

The plasmid vector pBR322 has both ampicillin and tetracycline resistance determinants. How would the resistance markers of this vector be used to identify recombinant plasmid molecules in a cloning experiment?

Answer 1

Answer:

Insertional inactivation of one antibiotic resistance gene would allow identifying the recombinant plasmid molecules by testing their susceptibility to the antibiotic.  

Explanation:

Let's suppose that the desired gene sequence is inserted into the gene sequence of the tetracycline resistance gene of the plasmid. This would render the recombinant plasmids susceptible to tetracycline. However, these recombinant plasmids would have resistance against ampicillin. Therefore, insertional inactivation of the tetracycline resistance gene would help to identify the recombinant plasmids from the non-recombinant ones.