Insertional activation is also a technique by which selection of recombinants can be done. In this process, …..(1)....... substrates are used as alternative selectable marker. For example, if a recombinant DNA is inserted into the coding sequence (or gene) of the 
-galactosidase enzyme in the plasmid of 
. coli, the gene become inactivated. In presence of …..(1)….substrate, …..(2)….will give blue colour while the …..(3)…..will give ……(4)…….colour.
(1) | (2) | (3) | (4) | |
(a) | Radioactive | Recombinants | Non-recombinants | Green |
(b) | Radioactive | Non-recombinants | Non-recombinants | No |
(c) | Chromogenic | Recombinants | Non-recombinants | Green |
(d) | Chromogenic | Non-recombinants | Recombinants | No |
Text Solution
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This question refers to insertional inactivation using chromogenic substrate (like X-gal) in blue-white screening.
1 = Chromogenic substrate (e.g., X-gal)
If recombinant DNA is inserted, β-galactosidase is inactivated, so:
Recombinants → do NOT produce blue colour (often white/colourless colonies)
Non-recombinants → produce blue colour (active β-galactosidase).
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