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Which is not consistent with double helical structure of DNA?

1. A = T, C = G
2. Density of DNA decreases on heating
3. A + T/C + G is not constant
4. Both A and B

Correct answer: Both A and B

Solution

In double-stranded DNA, adenine pairs with thymine and cytosine pairs with guanine, so A = T and C = G is consistent. Heating causes DNA to unwind and separate, which is not described by a decrease in density as a feature of the intact double helix; therefore both A and B are not consistent as stated.

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