Question

In the above represented plasmid an alien piece of DNA is inserted at the EcoRI site. Which of the following strategies will be chosen to select the recombinant colonies?

• A. Blue color colonies will be selected.
• B. White color colonies will be selected.
• C. Blue color colonies grown on ampicillin plates.
• D. Using ampicillin \& tetracyclin containing medium plate.

Hint:

In the blue/white screening method, the recombinant colonies are white because the insertion of foreign DNA disrupts the beta-galactosidase gene, preventing the conversion of X-gal to a blue color.

Answer 1

The Correct Option is B

In this case, the plasmid contains the beta-galactosidase gene, which is involved in the LacZ system. The EcoRI restriction site is where the foreign DNA is inserted. If the foreign DNA is inserted into the LacZ gene, it will disrupt its function and prevent the formation of beta-galactosidase, which normally converts X-gal into a blue product. - If the foreign DNA is inserted, the colonies will remain white (because LacZ is disrupted). - If no foreign DNA is inserted, the LacZ gene will remain intact, and the colonies will appear blue. Thus, recombinant colonies (with the foreign DNA inserted) will be white. The correct strategy is to select white color colonies.