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? 

The correct answer is White color colonies will be selected.

Concept:

• Plasmids are circular double-stranded DNA molecules used in molecular biology for genetic engineering and cloning purposes. They often carry selectable marker genes, such as antibiotic resistance genes, and restriction sites for insertion of foreign DNA.
• When a foreign DNA fragment is inserted into a plasmid at a specific restriction enzyme site (e.g., EcoRI site), the plasmid becomes recombinant.
• A common method for identifying recombinant plasmids is by using a process called blue-white screening, which is based on the disruption of the lacZ gene encoding β-galactosidase.

Explanation:

White color colonies will be selected:

• In blue-white screening, the lacZ gene in the plasmid is disrupted when a foreign DNA fragment is inserted at the EcoRI site.
• The disruption prevents the production of β-galactosidase, an enzyme responsible for converting X-gal (an artificial substrate) into a blue-colored product.
• As a result, colonies with recombinant plasmids appear white, while non-recombinant colonies (where lacZ is intact) appear blue. Selecting white colonies ensures that recombinant plasmids containing the alien DNA are identified.

Why Other Options Are Incorrect:

• Using ampicillin & tetracycline containing medium plate: While antibiotic selection (e.g., ampicillin resistance) is often used to ensure the presence of plasmids in transformed bacteria, this method does not distinguish between recombinant and non-recombinant plasmids. It only selects bacteria that contain the plasmid.
• Blue color colonies will be selected: Blue colonies indicate non-recombinant plasmids where the lacZ gene is intact and functional. These colonies do not contain the inserted alien DNA and are not the desired recombinants.
• Blue color colonies grown on ampicillin plates can be selected: Blue colonies represent non-recombinant plasmids. Additionally, while ampicillin selects for plasmid-containing bacteria, it does not distinguish between recombinant and non-recombinant colonies.