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WAEC Biology 2011 Question 60

Question 60

Chromosomes, DNA and Sex Linkage

Adenine pairs with thymine because

  1. A.the two occur in the same nucleic acid.
  2. B.one is a strong base and the other a weak base.
  3. C.two purine bases easily pair up.
  4. D.one is a purine base and the other a pyrimidine.
Show the answer and explanation

Answer: D (one is a purine base and the other a pyrimidine.)

Explanation

In DNA a purine (adenine) always pairs with a pyrimidine (thymine), which keeps the width of the double helix constant.