Erwin Chargaff's most famous experiment had to do with examining the components that make up DNA. His work with the different DNA bases proved that DNA remains the same within an organism but differs between different organisms. This contradicted previous scientific thought which had said that DNA was the same in all organisms and did not account for genetic diversity.
There are two different categories of bases found in the structure of DNA: purines and pyrimidines. Chargaff's most famous experiment established that these two types of bases appeared in a one-to-one ratio. There are four different bases: adenine, thymine, guanine and cytosine. Chargaff was able to prove with his experiment that there was a one-to-one ratio between adenine and thymine and a one-to-one ratio between guanine and cytosine.
Chargaff examined DNA from different organs within the same organism and found that the ratios of the different components in their DNA was consistent across organs and within individual organisms. However, when he looked at the ratios of DNA bases across different species, they differed; this allowed him to conclude that DNA composition is species-specific. Chargaff's experiments were important because James Watson, Francis Crick and Maurice Wilkins were later able to use the information he developed to discover the double-helix structure of DNA.