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NEET2026BiologyChapterActual

Biochemical analysis of a double-stranded DNA sample reveals that 18 % of its nitrogenous bases are Cytosine. Which of the following correctly represents the expected proportion of Adenine and Thymine in this sample?

Options

  1. A18 % Adenine and 18 % Thymine
  2. B64 % Adenine and 64 % Thymine
  3. C32 % Adenine and 32 % Thymine
  4. D32 % Adenine and 18 % Thymine

Correct answer

C. 32 % Adenine and 32 % Thymine

Step-by-step solution

According to Chargaff's rule for double-stranded DNA, the percentage of Adenine equals the percentage of Thymine, and the percentage of Guanine equals the percentage of Cytosine. Given that Cytosine ( C ) is 18 % , Guanine ( G ) is also 18 % . Total percentage of C + G = 18 % + 18 % = 36 % . The remaining percentage for Adenine and Thymine is 100 % - 36 % = 64 % . Since A = T , the percentage of Adenine ( A ) is 64 % 2 = 32 % and the percentage of Thymine ( T ) is 64 % 2 = 32 % . Answer: 32 % Adenine and 32 % Thymi

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