A) Chargaff discovered two rules that helped to reveal the structure of the double helicon DNA. Chargaff's rules claim that the DNA from any cell and any organism should have a 1: 1 ratio (base pair rule) of pyrimidine and purine bases, and more specifically that the amount of guanine is equal to the amount of cytosine, and the amount of adenine is equal to the amount of thymine. This form was found in both DNA strands.
B) James Watson and Francis Crick in 1953 proposed the first correct model of the double helicon DNA structure. Their model was based on only one X-ray diffraction image recorded by Rosalind Franklin and Raymond Gosling in May 1952, as well as information that the DNA bases ware paired, which came out of private communication with Erwin Chargaff during the previous years. Chargéff's rules played a very important role in determining the configuration of double helices for B-DNA as well as for A-DNA.
