Question

After insertion of DNA segment within the sequence of Z-gene of bacteria, they are grown on chromogenic substrate. After the growth of bacterial colonies, they are identified as
i) Recombinants if colonies are blue- coloured.
ii) Recombinants if colonies are white coloured.
iii) Non-recombinants if colonies are blue- coloured.
iv) Non-recombinants if colonies are white coloured.

• A. iii, iv
• B. i, iv
• C. i, ii
• D. ii, iii

Answer 1

The correct option is D ii, iii

• The z-gene controls beta-galactosidase enzyme as it is inserted on the DNA sequence it becomes inactivated by the process of insertional activation and the normal blue colour of cell culture with active beta-galactosidase will not appear but due to its absence, it will be of white coloured and will be of recombinant nature. However the non-recombinants formed were of blue colour.

So, the correct option is 'D'.