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Foundations Of Clinical Genetics Practice Test

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Which base pairs with cytosine in DNA?
Correct Answer:
Guanine
Explanation:
In DNA, bases pair in a very specific way to keep the double helix uniform and stable. Cytosine pairs with guanine because cytosine is a pyrimidine (a smaller base) and guanine is a purine (a larger base), together matching the width of the DNA ladder. This GC pair forms three hydrogen bonds, making it more stable than the adenine–thymine pair, which has two hydrogen bonds. Adenine pairs with thymine in DNA, while uracil is used in RNA and pairs with adenine. So, the base that pairs with cytosine is guanine.

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