If Guanine Makes Up 60% of the Bases in a DNA

Question

If guanine makes up 60% of the bases in a DNA double helix, what percent of the bases is adenine?
A)60%
B)40%
C)20%
D)50%

Accepted Answer

In a DNA double helix, adenine always pairs with thymine, and guanine always pairs with cytosine. Therefore, if guanine makes up 60% of the bases, then cytosine must also make up 60% of the bases. This means that the remaining 40% of the bases must be adenine and thymine. Since adenine and thymine are always present in equal amounts, adenine must make up 20% of the bases.