Foreign DNA insert within LacZ in the plasmid vector results in which of the following during Isopropyl B-D-1-thiogalactopyranoside (IPTG) along with X-gal for blue-white screening

O None of the answers are correct

O White Colonies

O Blue Colonies

O Randomly shows Blue or White Colonies.

O White Colonies

Explanation:

LacZ gene present in the plasmid vector encodes α subunit of enzyme β galactosidase while ω (omega) subunit of this enzyme is present in the E. coli itself. When plasmid is introduced into a mutant E. coli by a process known as transformation then ω (omega) subunit of β galactosidase is able to complement with α subunit resulting into active β galactosidase.

If foreign DNA insert will get incorporated in the plasmid vector then the colonies will remain white because lacZ gene has MSC (multiple cloning site) where foreign DNA gets incorporated leading to insertional inactivation of the gene as a result of which it will not be able to encode α subunit of enzyme β galactosidase. β galactosidase is a tetramer which is able to convert it's chromogenic substrate X gal into blue colored precipitate only if it has both α subunit and ω (omega) subunit. But due to insertional inactivation, α subunit does not get synthesized and β galactosidase fails to convert X gal into blue colored precipitate therefore only white colonies will be detected.