Final answer:
According to Chargaff's rules, the percentage of cytosine (C) in a DNA sample that contains 27% adenine (A) would be 23%, because A pairs with T and G pairs with C, and they must be equal for the DNA to maintain its structure.
Therefore, the percentage of cytosine (C) in the DNA would be 23%.
Step-by-step explanation:
If the DNA of a particular species contains 27 percent adenine (A), then according to Chargaff's rules, the amount of thymine (T) would also be 27 percent because A pairs with T. Since DNA is made up of pairs between adenine and thymine, and guanine (G) and cytosine (C), the percentage of cytosine can be calculated by subtracting the combined percentage of adenine and thymine from 100 percent. So, if A and T together account for 54 percent (27 percent A + 27 percent T), then G and C together would also have to account for 46 percent. With the question specifying only the percentage of adenine, we must assume that G and C are present in equal amounts to maintain the base pairing rule, which means cytosine would also be 23 percent.