A plasmid vector has a gene for erythromycin resistance (Ery") and a gene for ampicillin resistance (Amp"). The Ery gene is cut with restriction enzyme, and donor DNA treated with the same enzyme is added along with ligase. To find cells transformed by a vector containing the donor DNA insert, what antibiotic resistance phenotypes will you select and screen for?

Insertion of the desired gene sequence within the sequence of an antibiotic resistance gene makes the transformed cells to lose the resistance against that particular antibiotic. To create a recombinant plasmid vector, the sequence of the gene for erythromycin resistance was cut with the restriction enzyme. This would cause a loss of resistance against erythromycin in the transformed cells. Since the ampicillin resistance gene was intact, the transformed gene would exhibit resistance against ampicillin. Therefore, the transformed cells would be ampicillin-resistant and erythromycin sensitive.