Question

A lac operon mutant is grown in the presence and absence of lactose and tested for activity of the biosynthesis genes ‘Z’, ‘Y’, and ‘A’. Given the genotype below, which biosynthetic genes would be expressed in the presence of lactose?

I⁺ P⁺ O⁺ Z⁺ Y^- A⁺/ F’ I^- P⁺ O⁺ Z⁺ Y^- A⁺

Select one:

a. none

b. Z, Y, and A

c. P and O

d. Z and A

e. I, P, O, Z, Y, and A

Answer 1

The I+ gene is dominant over I-. In this way, the merodiploid has expression of I gene. Ut encodes repressor protein. The presence of lactose in the surrounding leads to bind the lactose to the repressor. In this way,the repressor becomes inactive in nature. It can not bind to the operator region. RNA polymerase binds to the promoter. And it will proceed further which leads to the expression of structural genes. Z encodea beta galactosidase, Y encodes permease and A encodes transacetylase.

Hence there is found expression of I ,P, O, Z, Y and A genes.

right answer is E.