Mutability of genes depends on their functional state - a hypothesis.

A new point of view is formulated on the main dogma of genetics - the undirectedcharacter of mutagenesis. In the study of spontaneous mutability in adenine auxotrophic strains of the yeast, Saccharomyces, it was shown that when diminishing the adenine concentration in the medium, the transition from repression to derepression of the adenine biosynthesis system is accompanied by a 1.5-2 orders of magnitude increase in the spontaneous mutation rate in the ade2 gene. At the same time the mutation rate of suppressor genes varies very little. On this ground the following hypothesis is proposed: active genes mutate much more often than repressed ones. Some consequences of this hypothesis are discussed.