The Austro-Hungarian biochemist, Erwin Chargaff, came up with what is now known as Chargaff's rules (which is comprised of two rules). In the first rule, Chargaff stated that DNA from any cell or organism would have a 1:1 ratio of pyrimidine and purine bases. This means that the number of guanine units would equal the number of cytosine units. The same thing goes between thymine and adenine units. This implicates the base pairing in DNA. This finding of Chargaff helps the conceptualization of the double helical structure of DNA as proposed by Watson and Crick. This also refuted the then-accepted notion that DNA would be comprised of a number of repeats of guanine, adenine, cytosine, and thymine.
The second rule proposed by Chargaff is that the amount of guanine, adenine, cytosine, and thymine would vary between species. This finding implicated that DNA instead of protein is the genetic material.