The three classes of triplet profiles of natural genomes.

Based on the huge variety of different genomes, one may expect a correspondingly large variety of the frequency distribution of their trinucleotides ("triplet profiles"). Yet, this article reports the unexpected finding that there are essentially only three kinds of triplet profiles among the large number of genomes examined here. None of the classes included random profiles, all of them contained members from vastly different taxa and species. Since the three classes of genomes do not reflect the phylogeny of their member organisms, I propose that these classes may reflect species-independent mechanisms of genome evolution.