Intra-tetrad mating and genomic organization -- We have focused on an intriguing mating system found in the anther-smut fungus, Microbotryum. This fungus mates among the products of a single meiosis. Intra-tetrad mating occurs in other fungi, in many insects, in some mosses, and is similar to meiotic parthenogenesis in plants and animals. Our fungal system has the advantage that we can isolate the linear tetrads by micro-manipulation for use in molecular analysis. We are testing the prediction that intra-tetrad mating can maintain heterozygosity with a consequent build-up of alleles that may be deleterious in the haploid stage, but may have benefits in the diploid stage by altering disease expression.