[Analysis of maintenance of redundant genetic structures in the yeast Saccharomyces cerevisiae: disomy and spontaneous mitochondrial rho(-)-mutability].

With the postmeiotic progeny of triploids used as initial material, n + 1 disomics at chromosomes II, III, VII, VIII, and X were isolated. Disomy at the chromosomes listed (as well as for chromosomes IV and XIV, as demonstrated previously) is associated with decreased spontaneous rho- mitochondrial mutability. This suggests that a disturbance of the chromosome balance itself as such can lead to considerable changes in the spontaneous variability of the mitochondrial genome. From crosses between n + 1 disomics at chromosome IV and for each of the remaining above-mentioned six chromosomes, double n + 2 disomics were isolated, carrying nonchromologous pairs of extra chromosomes. Analysis of mitotic stability of the chromosome IV and spontaneous rho- mutability in double disomics shows that the effect of disomy on spontaneous rho- mutability most probably cannot be explained by direct competition between different genetic structures maintained in Saccharomyces cerevisiae cells. Disturbance of the chromosome balance in disomy is accompanied by essential qualitative changes in processes mediating the maintenance of genetic structures in yeast cells.