ANALYSIS OF MAINTENANCE OF REDUNDANT GENE TIC STRUCTURES IN THE YEASTSACCHAROMYCES-CEREVISIAE - DISOMY AND SPONTANEOUS RHO(-) MITOCHONDRIAL MUTABILITY

With the postmeiotic progeny of triploids used as initial material, n + 1 disomics at chromosomes II, III, VII, VIII, and X were isolated. D isomy 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 th e chromosome balance itself as such can lead to considerable changes i n the spontaneous variability of the mitochondrial genome. From crosse s between n + 1 disomics at chromosome IV and for each of the remainin g above-mentioned six chromosomes, double n + 2 disomics were isolated , carrying nonchromologous pairs of extra chromosomes. Analysis of mit otic stability of the chromosome IV and spontaneous rho- mutability in double disomics shows that the effect of disomy on spontaneous rho- m utability most probably cannot be explained by direct competition betw een different genetic structures maintained in Saccharomyces cerevisia e cells. Disturbance of the chromosome balance in disomy is accompanie d by essential qualitative changes in processes mediating the maintena nce of genetic structures in yeast cells.