(a) Identify the selectable markers in the diagram of E. coli vector shown above.
(b) How is the coding sequence of -galactosidase considered a better marker than the ones identified by you in the diagram ? Explain.
(a) 'a' is ampR (Ampicillin resistance)
'b' is tetR (Tetracycline resistance).
(b) 1. Recombinants and non - recombinants are differentiated on the basis of their ability to produce colour in the presence of a chromogenic substrate.
2. In this a recombinant DNA is inserted within the coding sequence of -galactosidase. It inactivates the enzyme. This is called insertional inactivation.
3. Recombinants do not produce blue colour as rDNA is present in the plasmid which results into insertional inactivation of the -galactosidase.
4. Non -recombinants produce blue colour in presence of chromogenic substrate as the plasmid in the bacteria does not have rDNA.