Which of the following base compositions is possible for double-stranded DNA?

• A. A = 10%, T = 40%, G = 25%, C = 25%
• B. A = 30%, T = 30%, G = 20%, C = 20%
• C. A = 20%, T = 20%, G = 30%, C = 40%
• D. A = 35%, T = 15%, G = 25%, C = 25%

Answer: (B)

Verified step by step guidance

1. Recall Chargaff's rules, which state that in double-stranded DNA, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). This means \(A = T\) and \(G = C\).
2. Check each given base composition to see if the percentages of A and T are equal, and if the percentages of G and C are equal.
3. Verify that the total percentage of all four bases adds up to 100% for each option, since the sum of all nucleotide percentages must be 100%.
4. For each option, confirm both conditions: \(A = T\), \(G = C\), and \(A + T + G + C = 100\%\).
5. Identify the option(s) that satisfy both Chargaff's rules and the total percentage requirement, which indicates a possible base composition for double-stranded DNA.