Final answer:
In DNA, due to Chargaff's rules, the percentage of thymine is equal to the percentage of adenine. Since cytosine makes up 42% of a DNA sample, guanine will also be 42%, making thymine and adenine each 29% of the nucleotides.
Step-by-step explanation:
According to Chargaff's rules, in DNA, the percentage of cytosine (C) is equal to the percentage of guanine (G), and the percentage of adenine (A) is equal to the percentage of thymine (T). Since cytosine is 42% of the nucleotides in the DNA sample referenced in the question, it means that guanine will also be 42%. Therefore, the purines (A and G) will be 58% of the nucleotides (100% - 42% for C and 42% for G). Since A pairs with T, this means that adenine will also be 29%, and the percentage of thymine will be the same, 29%.
In DNA, cytosine (C) and thymine (T) are pyrimidines, while adenine (A) and guanine (G) are purines. According to Chargaff's rules, the amount of adenine always equals the amount of thymine, and the amount of cytosine always equals the amount of guanine. In the given DNA sample, cytosine makes up 42% of the nucleotides. Therefore, thymine will also make up 42% of the nucleotides because of the complementary pairing between cytosine and thymine.