Question

(a) Identify the selectable markers in the diagram of E. coli vector shown above.

(b) How is the coding sequence of a-galactosidase considered a better marker than the ones identified by you in the diagram? Explain.

Answer 1

(a) a–Ampicillin resistance 

 d–Tetracycline. 

(b) The insertion of rDNA into the coding sequence of an enzyme a-galactosidase leads to the inactivation of the enzyme called insertional inactivation. The recombinants do not produce a blue coloured colonies in the presence of chromogenic substrate while the non-recombinants produce a blue colour. Thus, coding sequence of a-galactosidase is a better marker.