SAT Subject Biology Practice Question 355: Answer and Explanation
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.