The blue and white selectable markers have been developed which differentiate recombinant colonies from non-recombinant colonies on the basis of their ability to produce colour in the presence of a chromogenic substrate. Given below are two statements about this method: In the light of the above statements, choose the most appropriate answer from the options given below:
- Statement I is correct but Statement II is incorrect
- Statement I is incorrect but Statement II is correct
- Both Statement I and Statement II are correct
- Both Statement I and Statement II are incorrect
Answer
(2) Statement I is incorrect but Statement II is correct
Solution
The DNA insert is placed within the coding sequence of the enzyme -galactosidase, which inactivates it (insertional inactivation).
Colonies without an insert have an active -galactosidase and give blue colour with the chromogenic substrate — so Statement I is incorrect.
Recombinant colonies (with insert) do not produce blue colour — so Statement II is correct.
Answer: (2)