Question

In DNA of certain organisms, guanine constitutes $20\%$ of the bases. What percentage of the bases would be adenine?

• A. $10\%$
• B. $20\%$
• C. $30\%$
• D. $40\%$

Answer 1

The correct option is C $30\%$

If guanine constitutes $20\%$ then the adenine would be $30\%$. According to Chargaff's rule, in DNA, the proportion of adenine always equals to that of thymine and proportion of guanine always equals to that of cytosine, i.e. A=T and G=C. Thus, in the DNA of an organism, if guanine is $20\%$ cytosine also will be $20\%$. So, both adenine and thymine together will be $60\%$, i.e. $30\%$ adenine and $30\%$ thymine.