In blue-white screening using lacZ alpha-complementation in a plasmid vector, what does a white bacterial colony on X-gal medium indicate?
- A The lacZ gene is disrupted by inserted foreign DNA ✓
- B The plasmid lacks an origin of replication
- C The bacteria are antibiotic-sensitive
- D The plasmid has lost the lacZ gene entirely
Correct answer: A. The lacZ gene is disrupted by inserted foreign DNA
Explanation
In blue-white screening, functional beta-galactosidase (from intact lacZ) cleaves X-gal to produce a blue product. When foreign DNA is inserted into the multiple cloning site within lacZ, the gene is disrupted, alpha-complementation fails, and colonies remain white. White colonies therefore indicate successful recombinant plasmids.
Reference: Molecular Cloning: A Laboratory Manual, 4th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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