Effects of elevation of strain-ploidy on transmission and recombination of mitochondrial drug resistance genes in Saccharomyces cerevisiae

Summary In order to study the effects of strainploidy on the transmission and recombination of the mitochondrial genes C, E and O conferring the resistance to chloramphenicol, erythromycin and oligomycin, respectively, haploids were crossed to diploids and the results of genetic analysis were compared with those from haploidxhaploid crosses. All haploidx diploid crosses showed an increased transmission of diploid derived alleles, relative to haploid derived ones, but the pattern of increase differed between homosexual and heterosexual crosses. In ^– haploid x ^– diploid homosexual crosses, the increase was of roughly equal magnitude at the C, E and O loci: there was a polar co-transmission of the diploid derived alleles. In ⁺ haploid x ^– diploid heterosexual crosses, on the contrary, a differential increase was observed at the different loci, the magnitude being the smallest at the C locus and the largest at the O locus. As a result, there was a preferential transmission in favor of the haploid derived C alleles and of the diploid derived O alleles. A near equal transmission from both parents was observed for the E alleles. A decrease and an increase in the recombination frequency were noticed in the above haploidxdiploid homosexual and heterosexual crosses, respectively.The above phenomena were ascribed to different dosages of mitochondrial genomes from parents. Experimental data were well accorded with the theoretical expectations which were obtained on the assumptions that diploids contain twice as many mitochondrial genomes as haploids, and that random pairing and recombination would occur among mitochondrial genomes from parents. The elevation of strain-ploidy did not affect the recombination polarity which is under the control of the gene.It was theoretically predicted that a preferential transmission in favor of diploid derived alleles at all the C, E and O loci would be seen in ^– haploid x ⁺ diploid heterosexual crosses as well as in ^+; haploid x ^+; diploid homosexual crosses, but that the magnitude of the polar transmission would vary depending upon the loci in the former crosses, while it would be the same at all the loci in the latter ones. The recombination frequency was predicted to decrease in both of these crosses.