2025 Biotechnology: Principles and ProcessesBlue-White Screening Method Easy Question 16 of 132 in Biotechnology: Principles and Processes

The blue and white selectable markers have been developed which differentiate recombinant colonies from non-recombinant colonies on the basis of their ability to produce colour in the presence of a chromogenic substrate.
Given below are two statements about this method:
Statement I: The blue coloured colonies have DNA insert in the plasmid and they are identified as recombinant colonies.
Statement II: The colonies without blue colour have DNA insert in the plasmid and are identified as recombinant colonies.
In the light of the above statements, choose the most appropriate answer from the options given below:

A Both Statement I and Statement II are correct
B Both Statement I and Statement II are incorrect
C Statement I is correct but Statement II is incorrect
D Statement I is incorrect but Statement II is correct

The answer is D.

Solution

Statement I is false; Statement II is true because insertional inactivation prevents color formation, yielding white recombinant colonies.

When foreign DNA is inserted into $\beta$-galactosidase, insertional inactivation prevents enzyme formation, leaving recombinant colonies white (uncolored). Plasmids without insert express active $\beta$-galactosidase and turn blue with chromogenic X-gal. Thus Statement I is incorrect and Statement II is correct.

Concept Insertional Inactivation Mechanism

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132 questions from this chapter have appeared across 26 exam years.