[Campbell Biology P.367] Which of the following statements best describes Chargaff's rules a... | Practice Question

Which of the following statements best describes Chargaff's rules as demonstrated by the sea urchin and salmon data in the table?

  • A: The percentages of adenine and guanine are always equal, and those of cytosine and thymine are always equal.
  • B: The sum of adenine and thymine percentages equals the sum of guanine and cytosine percentages for all species.
  • C: The percentage of adenine approximately equals that of thymine, and the percentage of guanine approximately equals that of cytosine, with these proportions varying among different species.
  • D: DNA from different species always has the same percentage composition of all four bases.

Explanation

Chargaff's rules, as described and demonstrated by the data, highlight two key points: 1 the amount of adenine A is approximately equal to thymine T , and the amount of guanine G is approximately equal to cytosine C ; and 2 these A/T and C/G ratios are consistently 1:1, but the overall percentages of these pairs vary from species to species.