"The science of molecular genetics began with the determination of the structure of DNA. Experiments with bacteria and
phages (i.e., viruses that infect bacteria) in the late 1940s and early 1950s, as well as the presence of DNA in
chromosomes of higher organisms, had implicated this macromolecule as the hereditary material (see the introduction).
In the 1930s, biochemical studies of the base composition of DNA by Erwin Chargaff established that the amount of
guanine always equals the amount of cytosine and that the amount of adenine always equals the amount of thymine,
independent of the total base composition of the DNA.
In the early 1950s, X-ray diffraction studies by Rosalind Franklin and Maurice Wilkins showed that DNA is a double helix.
Finally, in1953, Francis Crick and James Watson put together the chemical and X-ray diffraction information in their
famous model of the structure of DNA. This story is one of the most dramatic in the history of science and has been the
subject of many historical treatments, some of which are listed at the end of this chapter"--