Cambridge Physics - The Structure of DNA

The Origin of Species
James Watson
Bragg's Laboratory
Francis Crick
The Basics of DNA
X-ray photographs
Three-chained Failure
Pauling and Model Building
B Type DNA
Like-with-like Structure
Hydrogen Bonding
Chargaff's Rules
Finding the Flaws
A Working Model!
Living with a Double Helix

Bonding Bases

12. Chargaff's rules

This 'like-with-like' structure would suggest that the four bases could appear in any proportion, and not have any dependence on each other. One or more of the bases could be much more common than the others and there would be no correlation between the quantities of any two bases.

During 1952, while working on their other research in the Cavendish, Crick and Watson had spoken to the Austrian chemist Erwin Chargaff. Chargaff had recently published results showing that the abundance of the bases were not completely independent. Instead it seemed that adenine appeared in equal quantities to thymine, and cytosine appeared in equal quantities to guanine.

Chargaff had not offered any explanation for these results, but they were not consistent with Watson's like-with-like model.