Question:medium

plasmid an alien piece of DNA is inserted at the EcoRI site

In the above represented plasmid an alien piece of DNA is inserted at the EcoRI site. Which of the following strategies will be chosen to select the recombinant colonies?

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In the blue/white screening method, the recombinant colonies are white because the insertion of foreign DNA disrupts the beta-galactosidase gene, preventing the conversion of X-gal to a blue color.
Updated On: Nov 26, 2025
  • Blue color colonies will be selected.
  • White color colonies will be selected.
  • Blue color colonies grown on ampicillin plates.
  • Using ampicillin \& tetracyclin containing medium plate.
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The Correct Option is B

Solution and Explanation

The plasmid carries the beta-galactosidase gene, part of the LacZ system. Insertion of foreign DNA occurs at the EcoRI restriction site. Insertion into the LacZ gene disrupts its function, inhibiting beta-galactosidase production. Beta-galactosidase normally converts X-gal into a blue product. - Colonies with inserted foreign DNA will appear white due to LacZ disruption. - Colonies without inserted foreign DNA will retain an intact LacZ gene and appear blue. Therefore, recombinant colonies (containing foreign DNA) will be white. The optimal strategy involves selecting white colonies.
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