Question

If a dsDNA has $20\%$ adenine, what would be its cytosine content?

• A. $20\%$
• B. $30\%$
• C. $40\%$
• D. $80\%$

Answer 1

The correct option is B $30\%$

According to Chargaff’s rule, the DNA has equal ratio of pyrimidine (cytosine and thymine) and purine (adenine and guanine). In DNA, the number of adenine is equal to thymine, that is A = T. Similarly, the number of guanine is equal to cytosine, that is G = C. In the given problem, adenine content is 20%. Hence, thymine content will be 20%. Hence, the percentage of A + T content is 40%. The percentage of C + T content will be 60%. Out of this 60%, 30% will be cytosine content and remaining 30% will be guanine content.

Thus, the correct answer is option B.