Question: 115. In the above represented plasmid an alien piece of DNA is inserted at EcoRI site. Which of the following strategies will be chosen to select the recombinant colonies?
(1) Using ampicillin & tetracyclin containing medium plate.
(2) Blue color colonies will be selected.
(3) White color colonies will be selected.
(4) Blue color colonies grown on ampicillin plates can be selected.
Answer: Option (3)
Explanation:
The given plasmid contains the gene for β-galactosidase, which is involved in lactose metabolism and is used in blue-white screening.
The EcoRI restriction site lies within the β-galactosidase gene. When an alien DNA fragment is inserted at this site, it disrupts the β-galactosidase gene.
If the β-galactosidase gene is disrupted, the enzyme is not produced. As a result, such bacterial colonies cannot metabolize the chromogenic substrate and appear white on the medium.
Non-recombinant colonies have an intact β-galactosidase gene, produce the enzyme, and appear blue.
Therefore, recombinant colonies are identified and selected as white-colored colonies.
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