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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance1 Mark
MCQ
For question, two statements are given$-$one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes $(a), (b), (c)$ and $(d)$ as given below.
Assertion: Lactose in lac operon is promoter gene.
Reason: Lactose inactivates the repressor gene.
  • A
    Both assertion and reason are true, and reason is the correct explanation of assertion.
  • B
    Both assertion and reason are true, but reason is not the correct explanation of assertion.
  • C
    Assertion is true, but reason is false.
  • ✓
    Both assertion and reason are false
✓

Answer

Correct option: D.
Both assertion and reason are false
Lactose is not a promotor gene but an inducer of lac operon as it combines with repressor protein fanned by repressor or regulatory gene and not the gene itself. The inducer joins the repressor, forming a repressor$-$inducer complex. This complex prevents the repressor from binding with the operator gene of the operon. This frees the operator gene so that the $\text{RNA}$ polymerase can move from the promoter to the structural genes. The structural genes are then transcribed, forming a piece of polycistronic $\text{mRNA.}$ The latter is transcribed by $\text{tRNA}$ and ribosomes into enzymes.

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