The amount of purine is always equal to the amount of
pyramidine in a certain DNA molecule or can be written as:
[A] + [G] = [C] + [T]
where A is adenine, G is guanine, C is cytosine and T is
thymine
But according to Chargaff’s rule, the amount of Guanine
is equal to Cytosine, so that:
[G] = [C]
Hence,
[A] + [C] = [C] + [T]
Cancel [C]:
[T] = [A]
[T] = 22%
So that means:
[G] = [C] = 28%
So there is 28% Cytosine
