Question
Blue-white screening is based on the activity of :
This question was previously asked in
CUET PG 2026 Agri-Business Management Question Paper (25-Mar-2026) (Shift 2)
The correct answer is
$\beta$-galactosidase
Blue-White Screening Basis
Blue-white screening is a technique used in molecular biology to identify bacterial colonies that contain recombinant plasmids after transformation.
This method relies on the disruption of the lacZ gene, which encodes the enzyme $\beta$-galactosidase.
Mechanism of Action
- The lacZ gene product, $\beta$-galactosidase, is responsible for hydrolyzing a specific substrate, X-gal.
- When functional $\beta$-galactosidase is present, it cleaves X-gal, producing an insoluble blue pigment (5,5'-dibromo-4,4'-dichloro-indigo).
- In blue-white screening, insertion of foreign DNA into the multiple cloning site (MCS) within the lacZ gene disrupts the gene.
- This disruption leads to the production of non-functional $\beta$-galactosidase or no enzyme at all.
- Consequently, X-gal cannot be cleaved, and the bacterial colonies remain white.
Enzyme Activity
Therefore, the blue-white screening process is fundamentally based on the enzymatic activity of $\beta$-galactosidase.
In the provided options, the activity of $\beta$-galactosidase is the basis for this screening method.
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