A DNA Specimen That Contains 30% Guanine Contains How Much

Question

A DNA specimen that contains 30% guanine contains how much thymine?
A)15%
B)20%
C)30%
D)60%
E)The amount of thymine cannot be determined.

Accepted Answer

In DNA, guanine pairs with cytosine and thymine pairs with adenine. The total percentage of guanine and cytosine should be equal to the total percentage of thymine and adenine. Therefore, if a DNA specimen contains 30% guanine, it should also contain 30% cytosine. This means that the total percentage of guanine and cytosine is 60%. Since the total percentage of guanine and cytosine is equal to the total percentage of thymine and adenine, the total percentage of thymine should also be 60%, and thus the percentage of thymine is 20% (60% - 30% guanine - 10% cytosine). Therefore, the answer is B.