INFERRING THE GENETIC-BASIS OF INBREEDING DEPRESSION IN PLANTS

Recent progress in the genetic analysis of inbreeding depression in pl ants is reviewed. While the debate over the importance of genes of dom inance versus overdominance effect continues, the scope of inferences has widened and now includes such facets as the interactions between g enes, the relative abundance of major versus minor genes, life cycle s tage expression, and mutation rates. The types of inferences are class ified into the genomic, where many genes are characterized as an avera ge, and the genic, where individual genes are characterized. Genomic i nferences can be based upon natural levels of inbreeding depression, p urging experiments, the comparison of individuals of differing F (e.g. , prior inbreeding), and various crossing designs. Genic inferences ma inly involve mapping and characterizing loci with genetic markers, inv olving either a single cross or, ideally, several crosses. Alternative statistical models for analyzing polymorphic loci causing inbreeding depression should be a fruitful problem for geneticists to pursue.