The blue and white selectable markers have been developed which differentiate recombinant coloniesfrom non-recombinant colonies on the basis of theirability to produce colour in the presence of achromogenic substrate.

Explanation:

The blue-white screening technique uses a chromogenic substrate (e.g., X-gal) and a reporter gene (lacZ) to distinguish between recombinant and non-recombinant bacterial colonies.

• The lacZ gene encodes the enzyme β-galactosidase, which can cleave X-gal to produce a blue-colored product.
• Insertion of foreign DNA into the multiple cloning site (MCS) within lacZ disrupts the gene — this is known as insertional inactivation.

The result is as follows:

• Blue colonies: No DNA insert → lacZ active → β-galactosidase produced → X-gal cleaved → Non-recombinant
• White colonies: DNA insert present → lacZ disrupted → no β-galactosidase → X-gal not cleaved → Recombinant

Evaluation of Statements:

• Statement I: Blue colonies have DNA insert and are recombinant → Incorrect
• Statement II: White colonies have DNA insert and are recombinant → Correct