Austro-Hungarian biochemist famous for discovering two rules (Chargaff’s rules) that helped in the determining the double-helical structure of DNA. The first rule dictates that the number of adenine equals the number thymine (and the same for guanine-cytosine). The second rule states that the amount of the four bases of DNA vary from species to species, based on which, scientists were able to conclude that DNA, and not protein, is the genetic material.