In a cloning experiment, a foreign DNA is inserted into the coding sequence of the -galactosidase gene of a plasmid vector. The transformed bacteria are then plated on a suitable agar medium containing a chromogenic substrate. Which of the following correctly describes the colour of the colonies formed by the recombinant and non-recombinant bacteria?

Step-by-step solution

Insertion of a foreign DNA into the coding sequence of the -galactosidase gene leads to insertional inactivation of the enzyme. As a result, the recombinant bacteria cannot produce functional -galactosidase and fail to cleave the chromogenic substrate, thereby forming colourless (white) colonies. In contrast, non-recombinant bacteria have an intact -galactosidase gene, produce the functional enzyme, and cleave the chromogenic substrate to form blue coloured colonies. Answer: Recombinants: White colonies; Non-recomb