Question

A foreign DNA is inserted and lighted 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 to ampicillin and susceptible to tetracycline
C. They are resistant to tetracycline and susceptible to ampicillin
D. They are resistant to ampicillin and tetracycline

Answer 1

The gene cloning is the mechanism to assemble foreign DNA molecules into the suitable host to direct their replication. The foreign DNA molecules are known as recombinant DNA molecules and are procured from two different sources or organisms.

Complete answer:
The recombinant DNA molecules are inserted into suitable hosts and are transferred through suitable cloning vectors. The vectors are considered as the DNA molecules that are used as a medium or vehicle to carry and transfer foreign genetic material into other cell types. The main purpose of the vectors are that they are used as delivery systems of the recombinant DNA.
Among the different types of cloning vectors used in this technique is the pBR322cloning vector. It was one of the first widely used E.coli vectors. This was created in 1977 in the laboratory of Herbert Boyer at the University of California, San Francisco.
It is a type of plasmid vector which was used for the purpose of cloning. It contains the origin of replication, the rop gene. There are two sites of restriction enzymes that are also present and are HindIII and CIaI.
pBR322 contains genes for the resistance to antibiotics. It carries two antibiotic resistance genes which are for the antibiotic tetracycline and ampicillin. At particular restriction sites, the DNA insertion can cause the genes for tetracycline or ampicillin resistance to become inactive. This process is known as insertional inactivation. BamHI site of pBR322 is the site of tetracycline resistance. In case of insertion of a foreign DNA in BamHI site, susceptibility to tetracycline increases as the resistant gene is replaced. However, resistance to ampicillin is not altered as it is left active.
As the insertion does not cause any changes in the ampicillin resistance gene, the DNA molecules are still resistant to the ampicillin.

Hence, the correct answer is option (B).

Note: pBR322 serves as a commonly used vector for cloning systems.It contains several sites among which the BamHI site is related to the tetracycline antibiotic resistance gene. Due to insertion of recombinant or foreign DNA into the BamHI site, it becomes susceptible to tetracycline while it remains resistant to ampicillin.