Inverse PCR is performed for site-directed mutagenesis with complementary primers (having the desired mutation) using a plasmid having the cloned gene as template. The following statements were made regarding the above experiment.

A. PCR is followed by transformation of bacterial cells directly with the reaction mixture. A large number of the transformants will have the wild type gene.
B. The PCR mixture is treated with Dpn I and then used to transform bacterial cells. Most of the transformants will have the mutant gene.
C. PCR is followed by transformation of bacterial cells directly with the reaction mixture. None of the transformants will have the mutant gene.
D. The PCR mixture is treated with Dpn I and then used to transform bacterial cells. Half of the transformants will have the mutant gene.

Which one of the following options represents a combination of all correct statements?

Correct option is A

Explanation-

Statement A -  PCR is followed by transformation of bacterial cells directly with the reaction mixture. A large number of the transformants will have the wild type gene. - CORRECT
Without DpnI treatment, the parental (wild-type) plasmid is still present and will be efficiently transformed, leading to a high number of wild-type transformants.

Statement B -  The PCR mixture is treated with DpnI and then used to transform bacterial cells. Most of the transformants will have the mutant gene.  - CORRECT
DpnI digests the methylated (parental) DNA. The mutant PCR product (newly synthesized and unmethylated) remains and transforms the bacteria, resulting in mostly mutant colonies.

Statement C -  PCR is followed by transformation of bacterial cells directly with the reaction mixture. None of the transformants will have the mutant gene.  - INCORRECT
Even without DpnI, some mutant plasmids can be taken up, although the majority will be wild type. So saying none is too absolute.

Statement D -  The PCR mixture is treated with DpnI and then used to transform bacterial cells. Half of the transformants will have the mutant gene.    -   INCORRECT
After DpnI treatment, the majority (not just half) of transformants will have the mutant plasmid, as the wild-type is degraded.

Correct Answer: Option a - A and B