If bacteria transformed with a recombinant pUC18 plasmid produce white colonies when grown on plates containing ampicillin and Xgal, which of the following is least likely?
A) They produce functional fi- galactosidase that cleaves X- gal.
B) They carry a vector with the bla gene used as the selectable marker.
C) They carry a vector with a lacZ gene that has been disrupted and rendered nonfunctional.
D) They carry a vector that contains a DNA fragment inserted into the multiple cloning site.
E) They produce fi- lactamase that provides resistance to ampicillin.

Question

Quizplus · Accepted Answer

Bacteria producing white colonies on plates containing X-gal and ampicillin indicates that the lacZ gene has been disrupted by the insertion of a DNA fragment, preventing the production of functional β-galactosidase. This enzyme is responsible for cleaving X-gal and producing a blue product. Therefore, the presence of white colonies suggests that β-galactosidase is not functional in these bacteria.

If Bacteria Transformed with a Recombinant PUC18 Plasmid Produce White