Question

dna and rna structure
quiz complete
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what did chargaff discover while studying bases in the dna of organisms?
the bases in the dna of each organism were unique.
the ratios of thymine and adenine were similar, as were the ratios of guanine and cytosine.
the overall percentages of bases were different from one organism to the next.
there were equal amounts of all four bases in every organism, or 25 percent of each base.

Explanation:

Chargaff's rules state that in DNA, the amount of adenine (A) is equal to thymine (T), and the amount of guanine (G) is equal to cytosine (C). This means the ratios of thymine and adenine are similar, as are the ratios of guanine and cytosine. The first option is incorrect because while the sequence may be unique, the base - pairing rules (Chargaff's rules) are consistent. The third option is about overall base composition differences (which is true but not what the question is asking about Chargaff's discovery related to base - pairing ratios). The fourth option is wrong because the amounts of A = T and G = C, but not necessarily 25% each (total of A + T+G + C = 100%, but A = T and G = C, their individual percentages can vary as long as A = T and G = C).

Answer:

The ratios of thymine and adenine were similar, as were the ratios of guanine and cytosine.