Q.An antibiotic gene in a vector usually helps in the selection of

Step 1. Recall the mechanism. The chapter describes an antibiotic resistance marker as 'a gene that produces a protein that provides cells with resistance to an antibiotic', explaining that bacteria with transformed DNA can be identified by growing them on a medium containing that antibiotic - transformed cells (carrying the resistance gene) grow, while others do not.

Step 2. Distinguish 'competent' from 'transformed'. Competent cells (option a) are cells that have simply been treated (e.g. with calcium and heat-shock) so that they are physically capable of taking up DNA - this happens before the antibiotic-selection step, and an antibiotic marker does not identify competence itself, only whether uptake actually succeeded. …

Match the antibiotic-marker mechanism described in the chapter to exactly what it selects for, and distinguish 'competent' (pre-uptake), 'transformed' (post- …

• Confusing 'transformed cells' with 'recombinant cells' - an antibiotic marker alone cannot tell a genuine insert-carrying recombinant apart from an empty, self-ligated vector. …