In a cloning experiment, you use a vector that contains a lacZ gene as a selectable marker. If the competent cells are grown on X-Gal and IPTG, which colonies would contain chromosomal DNA?
A) The white colonies
B) The blue colonies
C) Half the total colonies
D) None of the colonies

Question

Quizplus · Accepted Answer

The lacZ gene in the vector encodes for an enzyme called β-galactosidase, which breaks down the substrate X-Gal and produces a blue color. However, when the substrate is not present, the cells can produce a white color. Therefore, colonies that produce a white color on X-Gal and IPTG must have the lacZ gene disrupted due to the insertion of the cloned chromosomal DNA. These colonies would contain the chromosomal DNA of interest. The blue colonies would contain the intact vector with the functional lacZ gene, and the cells without the vector would not grow on the selective medium. Therefore, the best choice is A, the white colonies.

In a Cloning Experiment, You Use a Vector That Contains