AIIMS 2019 Biology Gene Regulation MCQ Question

The regulator gene produces a repressor protein that binds to the operator region of the lac operon, effectively switching off the operon by preventing RNA polymerase from transcribing the structural genes responsible for lactose metabolism. Option A (structural gene) refers to the genes that encode proteins, which are not involved in the regulation process. Option C (operator gene) is the site where the repressor binds, but it does not itself switch off the operon; rather, it is the action of the repressor from the regulator gene that inhibits transcription. Option D (promoter gene) is the region where RNA polymerase binds to initiate transcription, and it does not play a direct role in switching off the operon.