According to Chargaff’s base pairing rules, if 15% of the DNA sample is made up of thymine, what percentage of the sample is made up of cytosine?
According to Chargaff's base pairing rules, the amount of adenine is equal to thymine, and the amount of guanine is equal to cytosine.
Since thymine makes up 15% of the DNA sample, adenine also makes up 15% of the sample (as they pair together).
Since adenine and guanine together make up 30% of the DNA sample (15% adenine + 15% thymine), the remaining 70% of the sample is made up of cytosine and guanine.
Since adenine and guanine must be equal in amount, each of them makes up half of the remaining 70%, which is 35%.
Therefore, cytosine makes up 35% of the DNA sample.