What is the role of selectable …

Selectable markers are essential to identify and eliminate non-transformants(no recombinant DNA), and selectively permitting the growth of the transformants (host cells bearing recombinant DNA).

Selectable marker-

• It helps in identifying and eliminating non transformants and selectively permitting the growth of the transformants.
• Transformation is a procedure through which a piece of DNA is introduced in a host bacterium.
• The genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are useful selectable markers for E. coli as the normal E. coli cells do not carry resistance against any of these antibiotics.
• Antibiotic resistance genes help in selecting recombinants from non-recombinants by a method called insertional inactivation where a recombinant DNA is inserted within the coding sequence of an enzyme β-galactosidase in the presence of a chromogenic substrate which results into inactivation of the enzyme.
• The presence of a chromogenic substrate gives blue colored colonies if the plasmid in the bacteria does not have an insert.
• Presence of insert results into insertional inactivation of the β-galactosidase and the colonies do not produce any colour, these are identified as recombinant colonies.