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In sea urchin DNA, which is double stranded, 17% of the bases were shown to be cytosine. The percentages of the other three bases expected to be present in this DNA are:

1. 17% A, 16.5% T, 32.5%
2. 17% A, 33%, T 33%
3. 8.5% A, 50% T, 24.5%
4. 34% A, 24.5%, T 24.5%

Correct answer: 17% A, 16.5% T, 32.5%

Solution

Given that 17% of the bases are cytosine, the other bases must be adenine and thymine. Since cytosine and thymine are complementary, the percentage of thymine must be 17% less than cytosine, which is 16.5%. Similarly, the percentage of adenine must be 17% more than cytosine, which is 32.5%.

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