The Smooth Evolution of the Universal Genetic Code. Main Episodes

The possible scenario of the origin and evolution of genetic code is proposed, being primarily implicated by the working hypothesis which states that the chronological order of amino acids evolutionary implementation monotonically correlates with their increasing mass. It fulfills the minimalistic claim of the smallest changes of the evolving system at increasing complexity, hereinafter called "the smooth evolution". The working hypothesis was postulated concerning the results of statistical analysis indicating a strong correlation between amino acid mass and the chosen parameters of contemporary genetic code, which are expected to change in a certain individual direction during the evolution of the initial genetic system. It was additionally supplemented by the most common hypotheses adopted from the literature, as stereochemical, 'frozen accident' and coevolutional. The developed scenario allows a detailed description of the twenty-two consecutive episodes of the history of code definition and the estimation of its dynamics. It reveals the main eras of evolution conditioned by the environmental and structural constraints. It also lets the estimation of the evolutionary frequencies of codon sense expansion, and redefinition. Dominating trends and amino acids were indicated. The underlying assumptions, limits, exceptions, and the future of the code evolution have been discussed.