[Campbell Biology P.367] Based on Chargaff's rules and the provided table, what are the appr... | Practice Question

Based on Chargaff's rules and the provided table, what are the approximate percentages of Guanine G and Cytosine C in Human DNA?

  • A: G ≈ 19.75%, C ≈ 19.75%
  • B: G ≈ 30.4%, C ≈ 30.1%
  • C: G ≈ 29.0%, C ≈ 29.0%
  • D: G ≈ 24.7%, C ≈ 26.0%

Explanation

For Human DNA, the percentage of Adenine A is 30.4% and Thymine T is 30.1%. According to Chargaff's rules, A roughly equals T, and G roughly equals C. The total percentage of all four bases must be 100%. So, A + T + G + C = 100%. Given A=30.4% and T=30.1%, A+T = 60.5%. Therefore, G+C = 100% - 60.5% = 39.5%. Since G roughly equals C, each would be approximately 39.5% / 2 = 19.75%.