The common presentation of the standard (`universal´) genetic code. All deviations from this code (Elzanowski and Ostell 2000) are thought to be the result of later mutations (Osawa et al. 1992, Knight and Landweber 2000b, Knight et al. 2001).
Shaded regions show codon families.

The common scheme of the genetic code (Alberts et al. 2002) contains 4³=64 codons, a three-dimensional matrix where each dimension  represents one of the three positions in the triplet code. Viewed this way, some patterns emerge: The first codon position seems to be correlated with amino acid biosynthetic pathways (Wong 1975, Taylor and Coates 1989), and to their evolution as evaluated by synthetic “primordial soup” experiments (Eigen 1977, Schwemmler 1994).The second position is correlated with the hydropathic properties of the amino acids (Crick 1968, Wolfenden et al. 1979, Taylor and Coates 1989), and the degeneracy of the third position could be related to the molecular weight or size of the amino acids (Hasegawa and Miyata 1980, Taylor and Coates 1989).