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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: $\text{Z-DNA}$ follows a zig$-$zag course.
Reason: $\text{Z-DNA}$ is left handed.
  • A
    Both assertion and reason are true, and reason is the correct explanation of assertion.
  • ✓
    Both assertion and reason are true, but reason is not the correct explanation of assertion.
  • C
    Assertion is true, but reason is false.
  • D
    Both assertion and reason are false.
✓

Answer

Correct option: B.
Both assertion and reason are true, but reason is not the correct explanation of assertion.
$\text{Z-DNA}$ is left$-$handed double helix with zig$-$zag back $-$bone, alternate purine and pyrimidine bases, single turn of $45 A$ length with $12$ base pairs and a single groove. Due to a different arrangement of molecules within $\text{Z-DNA}$ polymer, phosphate backbone follows a zig$-$zag course, while in $\text{B-DNA}$ it is regular. In $\text{Z-DNA}$, sugar residues have alternating orientation so that the repeating unit is a dinucleotide.

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