  Codon usage bias measure is defined through the mutual entropy calculation of
real codon frequency distribution against the quasi-equilibrium one. This
latter is defined in three manners: (1) the frequency of synonymous codons is
supposed to be equal (i.e., the arithmetic mean of their frequencies); (2) it
coincides to the frequency distribution of triplets; and, finally, (3) the
quasi-equilibrium frequency distribution is defined as the expected frequency
of codons derived from the dinucleotide frequency distribution. The measure of
bias in codon usage is calculated for 125 bacterial genomes.
