Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure because it requires simultaneous plating on two plates having different antibiotics. Therefore, alternative selectable markers have been developed which differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate.WHAT DOES IT MEAN ?

  • After the insertion of alien DNA, the recombinant plasmids lose the antibiotic resistance, that is they get inactivated. Whereas the non recombinants still have both the antibiotic resistance genes.
  • So now we know the di​fference between the recombinants and the non-recombinants, but to check this we need to plate these at the same time in different plates with the different antibiotic resistance genes.
  • We need to observe what is growing where and what is not growing so this is quite a tiring or time-consuming procedure.
  • Hence, other selectable markers have been developed which are much easier to use.
  • Since, they easily differentiate recombinants from the non-recombinants as the recombinants do not have the ability to produce colour in presence of a chromogenic substrate. Non-recombinants can produce colour.
That is explained in the same paragraph on page 200 of the NCERT Textbook for Biology Hope this helps :)

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