Question

The diagram given below shows a method of screening the transformed bacterial cells.

Explain how the differently coloured colonies help in identifying the transformed cells.

Answer 1

The method shown is Blue-White Screening - a common technique used in recombinant DNA technology.

1. Blue colonies: These colonies show that the bacteria do not have the recombinant plasmid because the lacZ gene is intact. This gene produces β-galactosidase, which breaks down X-gal and gives a blue colour.
2. White colonies: These colonies show that the bacteria contain the recombinant plasmid because the inserted gene disrupts the lacZ gene. As a result, β-galactosidase is not produced, and the colonies remain white.