CBSE Class 12-science Answered
Selection of recombinants due to inactivation of antibiotic coding gene is a laborious process as it requires:
(i) a vector with two antibiotic resistance markers
(ii) preparation of two kinds of media plates, each with one type of antibiotic.
Transformed cells are first plated on the antibiotic plate in which the antibiotic gene has not been insertionally inactivated (example: ampicillin) and incubated overnight for the growth of transformants. For selection of recombinants, these transformants are replica-plated on the plate containing second antibiotic plate (example, tetracycline) which got inactivated due to insertion of the gene). Non-recombinants grow on both the plates (one carrying ampicillin and the other carrying tetracycline) while recombinants will grow only on ampicillin plate.
This entire process is laborious and requires more time (two overnight incubation) as well. However, if we choose insertional inactivation of a marker that produces colour in presence of a chromogenic substance, we can easily distinguish between recombinants and non-recombinants on a single medium plate (containing one antibiotic and the chromogenic compound) after just overnight growth.