###### Asked in BiologyGeneticsBiochemistry

Biology

Genetics

Biochemistry

# If adenine makes up 20 percent of the bases in a dna double helix what percent of the bases are guanine?

## Answer

###### Wiki User

###### July 29, 2012 10:54AM

30 %.

Adenine pairs with thymine - therefore if 20% is A, another 20% percent will be T. Only two other bases are left, which form pairs: guanine and cytosine, in equal quantities. Therefore half of the remaining 60 percent will be guanine.

## Related Questions

###### Asked in Genetics

### If adenine make up 20 percent of the bases in a DNA double helix then what percent of the bases are guanine?

To answer this question, remember this: in DNA, adenine always
pairs with thymine, and cytosine always pairs with guanine. Also,
in a normal DNA molecule, all of the bases are paired.
If 20% of the bases in DNA are adenine, then it follows that
another 20% must be thymine, because adenine always pairs with
thymine. Adding both percentages up, we get 40% of the DNA bases
being adenine and thymine. That means the remaining 60% of the
bases in the DNA molecule are cytosine and guanine. Using the same
reasoning above, the proportions of cytosine and guanine must be
equal because cytosine always pairs with guanine. Therefore,
cytosine and guanine each compose 30% of the DNA molecule.