SAT Subject Biology Practice Question 355: Answer and Explanation

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Question: 355

5. The base composition of DNA varies from one species to another. Which of the following ratios would you expect to remain constant in the DNA?

A. Cytosine : Adenine
B. Pyrimidine : Purine
C. Adenine : Guanine
D. Guanine : Deoxyribose
E. Thymine : Guanine

Correct Answer: B


B The ratio of purines to pyrimidines should be constant because purines always bind with pyrimidines, no matter which ones they may be.

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