If the DNA percentage of thymine is $20 \%$, then what is the percentage of guanine?
If the DNA percentage of thymine is $20 \%$, then what is the percentage of guanine?
$20 \%$
$40 \%$
$30 \%$
$60 \%$
Solution
According to Chargaff's Rule, the DNA molecule should have an equal ratio of pyrimidine (cytosine and thymine) and purine (adenine and guanine). It means that the number of adenine molecules is equal to thymine molecules and the number of guanine molecules is equal to cytosine molecules.
A complement with $\mathrm{T}$, and $\mathrm{G}$ complement with $\mathrm{C}$.
Thus, $\mathrm{T}=\mathrm{A}=20 \%$.
And, $\mathrm{A}+\mathrm{T}=40 \%$
Since, $\mathrm{G}=\mathrm{C}$
and, remaining of $\mathrm{G}+\mathrm{C}=60 \%$
so, $\mathrm{G}=\mathrm{C}=30 \%$