Question

A foreign DNA is inserted and ligated at BamHI site of $pBR322$. Select the statement that stands true for non recombinant transformants.

• A. They are susceptible to both ampicillin and tetracycline
• B. They are resistant of ampicillin but susceptible to tetracycline
• C. They are resistant to tetracycline but susceptible to ampicillin
• D. They are resistant to both ampicillin and tetracycline

Answer 1

The correct option is B They are resistant of ampicillin but susceptible to tetracycline

pBR322 Plasmid pBR322 was one of the first plasmids used for the purpose of cloning. It contains genes for the resistance to tetracycline and ampicillin. Insertion of the DNA at specific restriction sites can inactivate the gene for tetracycline (an effect known as an insertional inactivation) or ampicillin resistance. Tetracycline site is also called as BamH1 site of pBR322. When a foreign DNA is inserted in BamH1 site, the DNA gets suceptible to tetracycline as the resistant gene is replaced . But the DNA is resistant to ampicillin as it is left active.

So the correct option is 'They are resistant of ampicillin but susceptible to tetracycline'