9305498 Silliker These experiments will determine the pattern of inheritance of mitochondrial genomes in the acellular slime mold Didymiym iridis (Ditmar) Fries (class Myxomycetes). The mitochondrial DNA of one strain of D. iridis will be characterized by cloning and restriction enzyme mapping. Mitochondrial DNA variation will be assessed within strains of the largest heterothallic interbreeding group by comparison of probe hybridization patterns between strains. Once probes diagnostic for a mitochondrial type are identified they will be used to follow the fate of mitochondria in crosses. The results will be interpreted with special attention to the probable relatedness of these strains based on mitochondrial restriction fragment length polymorphism, geographical origin, and nuclear isozyme and mating type data. Uniparental organelle inheritance is an emerging rule for organelle behavior. Transmittance patterns are a result of unequal parental contribution (anisogamy) or mating type control in isogamous organisms with binary mating systems. Heterothallic myxomycetes have multiple-allelic mating systems. The pattern of mitochondrial inheritance in the myxomycete Physarum polycephalum was found to be determined by a mating type hierarchy. Preliminary evidence suggests that this is not the case with D. iridis. When compatible strains (different mating types) were crossed, about half the individuals inherited one mitochondrial type and half the other type. Replicate crosses with ten strains will be made in all possible combinations and the pattern of mitochondrial inheritance will be determined by hybridization of strain diagnostic probes to DNA samples from individuals. %%% Determining the pattern of mitochondrial transmittance in Didymium should allow development of hypotheses about the mechanism of inheritance. One working hypothesis predicts that mitochondrial inheritance will be more tightly regulated in closely related strains. The results of this research could be of major importance to evolutionary genetics. The involvement of undergraduate students in the project will be beneficial to the training of molecular geneticists. ***
