If we define a genetic code as a widespread DNA sequence pattern that carries a 
message with an impact on biology, then there are multiple genetic codes. 
Sequences involved in these codes overlap and, thus, both interact with and 
constrain each other, such as for the triplet code, the intron-splicing code, 
the code for amphipathic alpha helices, and the chromatin code. Nucleosomes 
preferentially are located at the ends of exons, thus protecting splice 
junctions, with the N9 positions of guanines of the GT and AG junctions oriented 
toward the histones. Analysis of protein-coding sequences reveals numerous 
traces of tandem repeats, apparently formed by triplet expansion, which in 
effect is a genome inflation ``code''. Our data are consistent with the 
hypothesis that expansion of simple tandem repetition of certain aggressive 
triplets has been a characteristic of life from its emergence. Such expanding 
triplets appear to be the major factor underlying observed codon usage biases.