A section of DNA has 30% adenine. What percentage of the bases are guanine?

Answer and explanation

Correct answer: C. 20%

  1. Step 1: A pairs with T, so thymine is also 30%.
  2. Step 2: A + T = 60%, leaving 40% for C + G, which splits equally: guanine = 20%.
Answer
20%.
Why not the others: 30%: this is the thymine percentage. 40%: this would be cytosine plus guanine. 70%: this is 100% minus 30%.

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