Final answer:
Based on Chargaff's rules, if DNA has 27% cytosine, it will also have 27% guanine due to base pairing. The remaining 46% of the DNA represents the total for adenine and thymine, and since they are equal, the percentage of thymine is 23%.
Step-by-step explanation:
The question revolves around Chargaff's rules which are central to the structure of DNA. According to these rules, in any given DNA molecule, the percentage of adenine (A) is equal to the percentage of thymine (T), and the percentage of cytosine (C) is equal to the percentage of guanine (G). If a DNA molecule is composed of 27% cytosine, it must also be composed of 27% guanine due to these base pairing rules. Consequently, since the DNA molecule is a double helix, and the sum of the percentages of all four bases must add up to 100%, the percentage of adenine and thymine combined would constitute the remaining percentage.
To determine the percentage of thymine (T) specifically, we begin with the total percentage being 100% and subtract the percentages of cytosine (C) and guanine (G), which are both 27%. After the subtraction, we have 100% - 27% - 27% = 46%. This remaining percentage is the combined value of adenine and thymine. Given that adenine and thymine percentages are equal, we divide this number by 2 to find the percentage of thymine:
46% / 2 = 23%
Therefore, the percentage of thymine in the DNA is 23%, which corresponds to option C.