What is the purpose of a selectable marker in bacterial cloning?

What is the purpose of a selectable marker in bacterial cloning?

• A. Increase plasmid copy number
• B. Identify bacteria with plasmid by antibiotic resistance
• C. Elicit mutation
• D. Induce plasmid replication

Answer: (B)

A selectable marker in bacterial cloning provides a trait you can use to distinguish cells that have taken up the plasmid from those that haven’t. The typical marker is an antibiotic resistance gene, so when you plate transformed cells on a medium containing the matching antibiotic, only the bacteria carrying the plasmid survive and grow. This makes it much easier to identify and isolate the clones that actually contain the plasmid, which is essential because many cells in the population won’t take up the plasmid. The marker’s job isn’t to increase how many copies of the plasmid are present, nor to induce mutations or to directly drive plasmid replication; it simply enables selective growth under specific conditions to reveal which cells carry the plasmid.

A selectable marker in bacterial cloning provides a trait you can use to distinguish cells that have taken up the plasmid from those that haven’t. The typical marker is an antibiotic resistance gene, so when you plate transformed cells on a medium containing the matching antibiotic, only the bacteria carrying the plasmid survive and grow. This makes it much easier to identify and isolate the clones that actually contain the plasmid, which is essential because many cells in the population won’t take up the plasmid. The marker’s job isn’t to increase how many copies of the plasmid are present, nor to induce mutations or to directly drive plasmid replication; it simply enables selective growth under specific conditions to reveal which cells carry the plasmid.