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# If a Double Stranded Dna Has 20 per Cent of Cytosine, Calculate the per Cent of Adenine in the Dna - Biology

ConceptThe DNA Structure of Polynucleotide Chain

#### Question

If a double stranded DNA has 20 per cent of cytosine, calculate the per cent of adenine in the DNA

#### Solution

According to Chargaff’s rule, the DNA molecule should have an equal ratio of pyrimidine (cytosine and thymine) and purine (adenine and guanine). It means that the number of adenine molecules is equal to thymine molecules and the number of guanine molecules is equal to cytosine molecules.

% A = % T and % G = % C

If dsDNA has 20% of cytosine, then according to the law, it would have 20% of guanine.

Thus, percentage of G + C content = 40%

The remaining 60% represents both A + T molecule. Since adenine and guanine are always present in equal numbers, the percentage of adenine molecule is 30%.

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#### APPEARS IN

NCERT Solution for Biology Textbook for Class 12 (2018 to Current)
Chapter 6: Molecular Basis of Inheritance
Q: 2 | Page no. 125
Solution If a Double Stranded Dna Has 20 per Cent of Cytosine, Calculate the per Cent of Adenine in the Dna Concept: The DNA - Structure of Polynucleotide Chain.
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