Codon frequencies in coding regions

A more informative method to determine coding regions, takes advantage of the frequencies in which the various codons occur in coding regions. For example, the amino acids Leucine, Alanine and Tryptophan are coded by 6,4 and 1 different codons respectively. In a translation of a uniformly random DNA sequence, these amino acids should occur in the ratio 6:4:1, but in a protein they occur in a different ratio - 6.9:6.5:1. Therefore coding DNA is not random. Another example of the non-uniformity of coding DNA is the fact that A or T occurs in the 3^rd position of a codon in a rate over 90% (these statistics vary for different species).