# How does the watson-crick model of dna relate to chargaffs rule?

The nitrogenous bases of DNA include the purines adenine (A) and guanine (G), and the pyrimidines thymine (T) and cytosine (C). Chargaff's rule states that there is always a 1:1 ratio of purines to pyrimidines in DNA. More specifically, the $A =$T and the $G =$C.