(a) Name the selectable markers in the cloning vector pBR332 ? Mention the role they play.
(b) Why is the coding sequence of an enzyme -galactosidase a preferred selectable marker in
comparison to the ones named above ? (3 marks)
(a) Selectable markers in pBR322 :
Ampicillin resistance gene
Tetracycline resistance gene
Role of selectable markers. They help in identifying and eliminating non-transformants/non-
recombinants and selecctively permitting the growth of transformants and recombinants.
(b) (i) Using -galactosidase as selectable marker is a simpler process and less cumbersome.
(ii) In the presence of chromogenic substrates recombinants are colourless and non-recombinants
are blue in colour. Non-recombinants produce blue colour in the presence of chromogenic subs-
trate as the plasmid in the bacteria does not have rDNA.