Chargaff's+Rules


 * Chargaff's rules**  state that DNA from any cell of all organisms should have a 1:1 ratio of pyrimidine and purine bases and, more specifically, that the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. This pattern is found in both strands of the DNA. They were discovered by Austrian chemist Erwin Chargaff.



Chargaff Parity Rule 1
The first rule holds that a double-stranded DNA molecule globally %A = %T and %G = %C. The rigorous validation of the rule constitutes the basis of Watson-Crick pairs in the DNA double helix.

Chargaff Parity Rule 2
The second rule holds that globally both %A ~ %T and %G ~ %C are valid for each of the two DNA strands. This describes only a global feature of the base composition in a single DNA strand.

Relative proportions (%) of bases in DNA Both of Chargaff's rules are supported by the following table:
 * ~ Organism ||~ A ||~ T ||~ C ||~ G ||
 * Human || 30.9 || 29.4 || 19.9 || 19.8 ||
 * Chicken || 28.8 || 29.2 || 20.5 || 21.7 ||
 * Grasshopper || 29.3 || 29.3 || 20.5 || 20.7 ||
 * Sea Urchin || 32.8 || 32.1 || 17.7 || 17.3 ||
 * Wheat || 27.3 || 27.1 || 22.7 || 22.8 ||
 * Yeast || 31.3 || 32.9 || 18.7 || 17.1 ||
 * //E. Coli// || 24.7 || 23.6 || 26.0 || 25.7 ||