In the double-stranded DNA, percentage of adenine is 30%. Calculate the percentage of cytosine present in it?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 20%
In double-stranded DNA, A pairs with T and G pairs with C. So A = T and G = C (Chargaff’s rule), and the four add up to 100 per cent.
A = 30%, so T = 30%.
A + T = 60%, so G + C = 100% − 60% = 40%.
G = C, so C = 40% ÷ 2 = 20%.
Option (2) 30% — Incorrect. 30% is the share of thymine, which pairs with adenine.
Option (3) 40% — Incorrect. 40% is G and C together, not cytosine alone.
Option (4) 70% — Incorrect. 70% is everything except adenine; it forgets the base pairing.