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 plasmid shown in the image is a typical cloning vector that contains three key features:

1. Ampicillin resistance gene (bla) – highlighted on the circular map, which allows only cells that have taken up the plasmid to grow on plates containing ampicillin.

2. lacZ α fragment – positioned next to the multiple‑cloning site (MCS) and indicated by the label “lacZ α” in the diagram. This fragment complements the host’s lacZ ω fragment, restoring β‑galactosidase activity.

3. EcoRI restriction site – marked by an arrow within the MCS. The alien DNA fragment is inserted precisely at this EcoRI site.

Because the foreign DNA is ligated into the EcoRI site within the lacZ α region, the α‑peptide is disrupted. As a result, cells that carry the recombinant plasmid cannot produce functional β‑galactosidase.

When the transformed cells are plated on medium that contains:

• Ampicillin (to select for plasmid uptake)
• IPTG (to induce lacZ expression)
• X‑gal (a chromogenic substrate for β‑galactosidase)

the following outcomes occur:

• Colonies with an **intact** lacZ α fragment (non‑recombinant plasmids) produce β‑galactosidase, cleave X‑gal, and appear **blue**.
• Colonies with a **disrupted** lacZ α fragment (recombinant plasmids) lack β‑galactosidase activity, so X‑gal remains uncut and the colonies appear **white**.

Therefore, to isolate the recombinant clones that contain the alien DNA inserted at the EcoRI site, the appropriate selection strategy is to pick the **white colonies** on the ampicillin‑IPTG‑X‑gal plates.