Question

When we ligate a foreign DNA at the Sal I site of $pBR322$, the $A$___ plasmid will lose tetracycline resistance due to the insertion of foreign DNA, but can still be selected out from $B$___ ones by plating the $C$___ on ampicillin containing medium.

• A. A = non-recombinant , B = recombinant , C = transformant
• B. A = recombinant , B = non-recombinant , C = transformant
• C. A = transformant , B = non-recombinant , C = recombinant
• D. A = recombinant , B = transformant , C = non-recombinant

Answer 1

Answer: (B)

pBR322 is an E.coli plasmid that contains the origin of replication, ampicillin-resistant gene, tetracycline resistance gene and multiple cloning site. It is a highly studied plasmid vector. Because it has two resistance genes, transformed cells can be screened from non-transformed by the process of insertional inactivation in which target DNA when inserted into tetracycline gene, disrupt the gene and making cell recombinant with resistance to ampicillin only. Hence, colonies formed on the ampicillin plate are those which contain target DNA.