THE ROLE OF ROBUSTNESS AND CHANGEABILITY ON THE ORIGIN AND EVOLUTION OF GENETIC-CODES

We propose that an essential factor on the origin of genetic codes is a balanced accomplishment of robustness and changeability, two antithe tical, hut fundamental, properties for the survival and evolution of o rganisms. These measures are defined as the intrinsic properties of ge netic codes. An evaluation of these properties explains the structural regularity of genetic codes, estimates the order of codon reassignmen t ire deviant codes, and predicts the most probable deviant codes that exist. The enumeration of genetic codes that could have evolved from the standard genetic code under the selection pressure on robustness a nd charageability strongly limits the freedom of codon reassignments. The codon reassignments of all currently known deviant genetic codes b elong to this predicted evolutionary path, and they generally give the highest improvements on robustness and changeability.