In the represented plasmid (with Ori, amp^R and tet^R resistance genes, and the β-galactosidase gene at the EcoRI site), an alien…

Question

In the represented plasmid (with Ori, amp^R and tet^R resistance genes, and the β-galactosidase gene at the EcoRI site), an alien piece of DNA is inserted at the EcoRI site.

Which of the following strategies will be chosen to select the recombinant colonies?

1. A. Using ampicillin & tetracycline containing medium plate
2. B. Blue color colonies will be selected
3. C. White color colonies will be selected (Correct answer)
4. D. Blue color colonies grown on ampicillin plates can be selected

Correct Answer

Option C — White color colonies will be selected

Detailed Solution & Explanation

The correct answer is White color colonies will be selected.

Key Points

• The alien DNA is inserted into the $\beta$-galactosidase gene at the EcoRI site, causing insertional inactivation of that gene.
• Non-recombinants (intact $\beta$-galactosidase) produce blue colonies; recombinants cannot make the enzyme and produce white colonies.
• Hence recombinant colonies are selected as the white ones (blue-white screening).