Cytoplasmic inheritance in Saccharomyces cerevisiae: comparison of first zygotic budsite to mitochondrial inheritance patterns.

Zygotic first budsite in Saccharomyces cerevisiae was studied in relation to defined mitochondrial inheritance systems: both petite and drug resistance. It was hypothesized that a highly asymmetric inheritance pattern would be correlated to a high frequency of first budsites on the petite or drug resistant end of the zygote (i.e., that portion of the zygote which was originally the drug resistant or petite haploid before zygote formation). The data collected did not support the hypothesis. For drug resistance, the budsite pattern is identical for a highly biased and a moderately biased inheritance pattern. In a grande by grande cross there is a high probability of the first bud appearing on the conjugation bridge, with lower but equal probabilities of the first bud appearing on one end or the other of the zygote. A grande by petite cross changes this pattern to a high probability of the first bud appearing on the grade end of the zygote, with a lesser probability of the first bud appearing on the conjugation bridge and virtually no budding of the petite end. This phenomenon is independent of degree of neutrality or suppressiveness of the petite strain used, however. The difference between a grande and a grande by petite pattern may be due to the relative functional ability of the mitochondria in each end of the zygote. Tests using antimitochondrial drugs suggest that selection of first budsite on a zygote is a complex phenomenon, not simply dependent upon mitochondrial phenotype. In conclusion, selection of the first zygotic budsite appears to be independent of mitochondrial inheritance patterns.