Question

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?

Options

• Using ampicillin and tetracyclin containing medium plate.

• Blue colour colonies will be selected.

• White colour colonies will be selected.

• Blue colour colonies grown on ampicillin plates can be selected.

Answer 1

White colour colonies will be selected.

Explanation:

The plasmid shown contains:

amp^R gene: for ampicillin resistance

tet^R gene: for tetracycline resistance

LacZ gene (β-galactosidase) interrupted at the EcoRI site

Insertional inactivation prevents the production of β-galactosidase when foreign DNA is inserted at the EcoRI site in the LacZ gene. If the bacteria’s plasmid lacks an insert, the addition of a chromogenic substrate results in blue-colored colonies. When an insert inactivates the β-galactosidase gene, the colonies are known as recombinant colonies because they don’t produce any colour. The tetracycline and ampicillin resistance genes in the provided DNA won’t change. As a result, the provided DNA will exhibit tet^R and amp^R resistance.