# When decoding the potato genome, it was found that the fraction of nucleotides with cytosine in a fragment of a DNA molecule is 20%

When decoding the potato genome, it was found that the fraction of nucleotides with cytosine in a fragment of a DNA molecule is 20%. Using Chargaff’s rule, which describes the quantitative ratios between different types of nitrogenous bases in DNA (G + T = A + C), calculate the amount (in%) in this sample of nucleotides with thymine.

Adenine (A) is complementary to thymine (T), and guanine (G) is complementary to cytosine (C), therefore the number of complementary nucleotides is the same; Chargaff’s rule: (A + T) + (G + C) = 100%
By condition C = 20%
A + T = 100% – (20% + 20%) = 60%
T = A = 60%: 2 = 30%

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