Question

In a DNA, the percentage of thymine is 20. What is the percentage of guanine in it?

• A. ( 20\% )
• B. ( 40\% )
• C. ( 30\% )
• D. ( 60\% )

Answer 1

The Correct Option is C

According to Chargaff's rules for DNA base pairing: The amount of adenine is always equal to the amount of thymine (T). The amount of guanine (G) is always equal to the amount of cytosine . The sum of the percentages of all four bases (A, T, G, C) is 100%. Given that the percentage of thymine (T) is 20\%. Therefore, the percentage of adenine is also 20\% (since A = T). The combined percentage of adenine and thymine is (20\% + 20\% = 40\%). The remaining percentage must be made up of guanine and cytosine: Percentage of (G + C) = (100\% - 40\% = 60\%). Since the amount of guanine (G) is equal to the amount of cytosine , the percentage of guanine is half of the combined percentage of G and C: \[ Percentage of guanine (G) = ( \frac{60\%}{2} = 30\% ). \]