A plasmid contains a multiple cloning site inside the coding region of the lacZ gene and also contains an ampicillin resistance gene at a separate locus. When cells are transformed with a successfully recombinant plasmid containing a piece of DNA cloned into the multiple cloning site, what color will the colonies be when grown on an agar plate containing ampicillin and X-gal?

(a.) green
(b.) white
(c.) colonies will not grow
(d.) blue
(e.) clear

The correct answer is option b, that is, white.

Explanation:

In the presence of the recombinant plasmid within the colonies disruption of lac z gene takes place, which results in no production of the beta-galactosidase enzyme. Due to the non-existence of the beta-galactosidase enzyme, the colonies remain white.  

This appearance of blue color in the colonies takes place when the enzyme beta-galactosidase reacts with the substrate X-gal. Thus, in the absence of beta-galactosidase, no reaction occurs and the colonies remain white.