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Erwin Chargaff was working at Columbia University in New York in the 1940s when he read Oswald Avery's research about DNA being the hereditary material. From that moment in 1944 he devoted his research to working out the chemical composition of DNA. He commented on this many years later at a commemoration of 100 years of nucleic acid research. He said, "Avery gave us the first text of a new language, or rather, he showed us where to look for it. I resolved to search for this text."
Chargaff's work is a vital part of the story of the history of genetics, not only because it shed more light on the function and properties of DNA, but because it ultimately contributed to the groundbreaking work of Crick and Watson.
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What are Chargaff's Rules?
His lab abandoned all other research and focused solely on DNA. At the time the tetranucleotide hypothesis was doing the rounds. It said that DNA was made up of four bases (adenine, thymine, guanine and cytosine) that were present in regular amounts, but that their organisation was too simple to carry hereditary information. It was Chargaff's work that overturned this.
By looking at the composition of DNA from various organisms i.e. plants, people and fish, Chargaff noticed that in any given species the ratio of adenine to thymine was roughly equal, and the ratio of cytosine and guanine was also roughly equal. For example in human DNA the ratios are; A=30.9%, T=29.4%, G=19.9% and C=19.8%. This rule is the same for every living thing. He had managed to show that the chemical bases exhibited a complementary relationship.
Even though Chargaff made this discovery and published the research in 1950, the significance of these base-pairs (he did not use that phrase) was to elude him. It wasn't until Crick and Watson's paper on the structure of DNA three years later that it was fully understood. In fact they cited his work in their landmark paper.
One of his other major observations was that the composition of DNA varied from species to species, in particular the ratios of the chemical bases.
Both these observations are now known as Chargaff's Rules, and it is likely that without them Crick and Watson's work would not have been possible. In fact both did pay tribute to the debt they owed to Chargaff's research.
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Source Chagraff's Quote: P and S Fall 2003; Vol 23, No 3
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There are more Brighthub articles on the history of Genetics;
Read about Oswald Avery's work here .....
.... and the genetics timeline here