Correspondence between mutation and selection pressure and the genetic code degeneracy in the gene evolution

There are three main elements deciding about the effect of mutations on the protein coding sequences-the type of the substitution of nucleotide, the selection for the function of the gene product and the nature of the genetic code itself. Selection used to be considered as the only directional process among the evolutionary mechanisms. In fact the mutational pressure is also “directional” which means that the rates of particular nucleotide substitutions tend to produce a DNA molecule with a specific nucleotide composition. Using Monte Carlo simulations we have shown that the genetic code plays the central role in buffering the effect of mutations and that all three elements are optimised in the generation of the genetic diversity in such a way that deleterious effects of mutations are substantially reduced.