In the majority of sexual eukaryotes, mitochondria are inherited predominantly from a single, usually the female, parent Like the majority of higher plants and animals, the pathogenic yeast Cryptococcus neoformans has two mating types (sexes), however, these two sexes are morphologically similar. In this study, I examined the distribution of the mating types and how mating types influence the inheritance of mitochondria in C. neoformans. My survey of mating type alleles in 358 isolates collected from four geographic areas in the US showed a biased distribution of mating type alleles with most isolates containing mating type a alleles. To characterize the role of mating type locus on mitochondrial inheritance, I constructed two pairs of congenic strains that differed only at the mitochondrial genome and mating type locus. Mating between these two pairs of strains demonstrated that uniparental inheritance in C. neoformans was controlled by the mating type locus and progeny predominantly inherited mitochondria from the mating type a parent. Specifically, we identified two genes within the mating type locus, SXIIa in mating type a strain and SXI2a in mating type a strain, that control mitochondrial inheritance. Disruption of these two genes resulted in biparental mitochondrial inheritance in sexual crosses. These two genes are the first ones identified capable of controlling uniparental mitochondrial inheritance in any organism. In addition, we determined that the deletion of the SXIIa gene enhanced the spread of mitochondrial introns in sexual crosses. This discovery is consistent with the hypothesis that uniparental lnheritance might have evolved to prevent the spread of selfish cytoplasmic elements. / Thesis / Doctor of Philosophy (PhD)