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Q.
In the $DNA$ double helix, purine always paired with pyrimidine base through H-bonds, that leads to
Molecular Basis of Inheritance
Solution:
The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs (bp). Adenine forms two hydrogen bonds with Thymine from opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds. As result, always a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two strands of the helix