Final answer:
In DNA, the percentage of guanine is equal to cytosine, and adenine is equal to thymine. Therefore, if guanine is 25%, cytosine is also 25%, and adenine and thymine are each 25%. For a DNA sample with 30% adenine, thymine is also 30%; if there's 22% thymine, then adenine is 22%, and guanine and cytosine are each 28%.
Step-by-step explanation:
According to Chargaff's rules, in a DNA double helix, the amount of guanine (G) will be equal to the amount of cytosine (C), and the amount of adenine (A) will be equal to the amount of thymine (T). Thus, if guanine makes up 25% of the bases, then cytosine also makes up 25% of the bases due to their pairing. Consequently, the remaining 50% of the bases are divided equally between adenine and thymine, meaning adenine will be 25%, and thymine will also be 25%.
Under the specific case where 30% of the bases within a DNA molecule are adenine (A), it follows that thymine (T) also constitutes 30% of the bases, adhering to Chargaff's rule. Therefore, the correct answer to the multiple-choice question is C. 30%.
When a DNA sample has 22% thymine, it implies that there is also 22% adenine. The remaining percentage of the DNA is then divided equally between guanine and cytosine, which together make up 56% (100% - 22% - 22%). This means guanine and cytosine each make up 28% of the bases.