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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance1 Mark
Question
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.
  1. Both assertion and reason are true, and reason is the correct explanation of assertion.
  2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
  3. Assertion is true, but reason is false.
  4. Both assertion and reason are false.
Assertion: Z-DNA follows a zig-zag course.
Reason: Z-DNA is left handed.
✓

Answer

  1. Both assertion and reason are true, but reason is not the correct explanation of assertion.

Explanation:

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 Z - DNA polymer, phosphate backbone follows a zig-zag course, while in B - DNA it is regular. In Z - DNA, sugar residues have alternating orientation so that the repeating unit is a dinucleotide.

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