Why are both selection and screening needed?

Correct answer: Selection chooses transformants and screening identifies recombinants

Selection and screening answer two different questions in recombinant DNA work. Selection uses a selectable marker, commonly resistance to a particular antibiotic, to allow cells carrying the vector to grow while non-transformants are inhibited. It therefore identifies likely transformants, but a selected cell may contain an empty vector or an incorrect construct. Screening then examines the surviving colonies to identify those with the desired insert or orientation, using methods such as colony PCR, restriction analysis, color-based indicators, or sequencing. Thus option A is correct; the other choices do not describe either procedure.