Principles of Genetics and Breeding

1.2.3.2 Base pair analysis

• Erwin Chargaff (1950) of Columbia University, New York was another very important contributor.
• Chargaff carried out a lengthy series of chromatographic studies of DNA samples from various sources and showed that, although the values are different in different organisms, the amount of adenine and thymine were always equal, as were the amount of guanine and cytosine.
• These findings, known as Chargaff's rules or base-pairing, provided a valuable confirmation of Watson and Crick's model.
• The most crucial piece of the puzzle came from an X-ray diffraction picture of DNA taken by Franklin in 1952, a picture that Wilkins shared with James Watson over dinner in London on January 30, 1953.
• Franklin's X-ray work strongly suggested that DNA was a helix.