Question

If a species contains 23% adenine in its DNA, what is the percentage of guanine it would contain?

Options

• 23%

• 46%

• 44%

• 27%

Answer 1

27%

Explanation:

To find the percentage of guanine, we use Chargaff's Rule, which states that in double- stranded DNA, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). Since adenine is 23%, then thymine must also be 23%, making the total for A + T equal to 46%. The remaining 54% (100% − 46%) must be shared equally between guanine and cytosine. By dividing this remaining amount by two (54% + 2), we find that the DNA contains 27% guanine.