Genetic analysis of unequal transmission of the mitochondrial markers in Saccharomyces cerevisiae.

The presence of mitochondrial sex factor, omega, was demonstrated in haploid strains of yeast Saccharomyces cerevisiae which came from our laboratory. Transmission and recombination of the mitochondrial genes (CR/CS, ER/ES and OR/OS), conferring the resistance/sensitivity to chloramphenicol, erythromycin and oligomycin, respectively, were non-polar in homosexual crosses and highly polar in heterosexual crosses. Different results were obtained in crosses involving an erythromycin resistant mutant G706E11 (CSEROS) which was found to contain cellular DNA of diploid level. This strain was omega- and showed no alleles from G706E11 (CS, ER and OS) were transmitted to the zygote progeny in preference to the CR, ES and OR alleles. When crossed to omega+ haploid strains, there was a highly polar recombination, but no transmission was seen for the E and O alleles. Polar transmission of markers from omega+ haploid parental strain, characteristic of heterosexual crosses, was noticed only for the C allele. The crosses of G706E11 to omega+ haploids featured an increase in the recombination frequency. The values of % suppressiveness of sigma- petite mutants were relatively low when determined by crossing to G706E11 or to sigma+ diploid strain M2-8C rather than by crossing to sigma+ haploid strains, indicating that there is a positive correlation between the polar transmission of drug resistance markers and the suppressiveness degrees. Genetic mechanism of the anomalous behaviors if mitochondrial genes in crosses involving G706E11 was discussed and interpreted as due to an unbalanced supply of mitochondrial genomes from parental strains.