Evolution of genetic codes through isologous diversification of cellular states

Evolution of genetic codes is studied as change in the choice of enzymes th at are used to synthesize amino acids from the genetic information of nucle ic acids. We propose the following theory: the differentiation of physiolog ical states of a cell allows for a choice of enzymes, and this choice is la ter fixed genetically through evolution. To demonstrate this theory a dynam ical systems model consisting of the concentrations of metabolites, enzymes , amino acyl tRNA synthetase, and tRNA-amino acid complexes in a cell is in troduced and studied numerically. It is shown that the biochemical states o f cells are differentiated by cell-cell interactions, and each differentiat ed type starts to use a different synthetase. Through the mutation of genes , this difference in the genetic code is amplified and stabilized. The rele vance of this theory to the evolution of non-universal genetic code in mito chondria is suggested. The present theory is based on our recent theory of isologous symbiotic speciation, which is briefly reviewed According to the theory, phenotypes of organisms are first differentiated into distinct type s through the interaction and developmental dynamics, even though they have identical genotypes: later with mutation in the genotype, the genotype als o differentiates into discrete types, while maintaining the "symbiotic" rel ationship between the types. Relevance of the theory to natural as well as artificial evolution is discussed.