After cloning, colony PCR is used for which purpose?

• A. Determines antibiotic resistance profile of colonies.
• B. Sequencing the entire plasmid in colonies.
• C. Quick screen to confirm presence of insert in bacterial colonies.
• D. Isolates plasmids from colonies for purification.

Answer: (C)

Colony PCR is used to quickly check whether a bacterial colony carries the recombinant plasmid with the insert. By picking a colony and running PCR with primers that flank the cloning site (one in the vector and one in the insert, or two primers around the insertion junction), you get a product only if the insert is present. If the insert is there, the amplified fragment is larger and matches the expected size; if not, you see a smaller, vector-only product. This rapid screen lets you identify colonies likely containing the desired recombinant plasmid without first purifying plasmid or sequencing, saving time before further verification. It isn’t a method to determine antibiotic resistance, sequence the entire plasmid, or purify plasmids.