<P> Chargaff's rules state that DNA from any cell of all organisms should have a 1: 1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine . This pattern is found in both strands of the DNA . They were discovered by Austrian born chemist Erwin Chargaff, in the late 1940s . </P> <P> The first rule holds that a double - stranded DNA molecule globally has percentage base pair equality:% A =% T and% G =% C. The rigorous validation of the rule constitutes the basis of Watson - Crick pairs in the DNA double helix model . </P>

Who discovered that adenine always matches with thymine