In an E.coli strain i gene gets mutated and its product can not bind the inducer molecule. If growth medium is provided with lactose, what will be the outcome ?

1. RNA polymerase will bind the promoter region

2. Only z gene will get transcribed

3. z, y, a genes will be transcribed

4. z, y, a genes will not be translated

Doubtly Asked 30 Oct 2026 NEET UG 2022 Practice test neet Save WhatsApp Report

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Answer: 4. z, y, a genes will not be translated

Key idea: If the repressor (product of the i gene) cannot bind the inducer, it stays bound to the operator.

Lactose (the inducer) is present, but the mutant repressor cannot bind it.
The repressor therefore keeps sitting on the operator and blocks RNA polymerase.
So the structural genes z, y, a are not transcribed, and hence not translated.

Options 1, 2 and 3 all imply some transcription. Option 4 is the outcome.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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