Partitioning of population genetic variance under multiplicative-epistaticgene action

Determining the way in which different QTLs interact (epistasis) in their e ffects on the phenotype is crucial to many areas in population genetics and evolutionary biology. For example, in the founder event, a separated popul ation readapts to a new environment through the release of cryptic gene-gen e interactions. In hybrid zones, hybrid speciation must be subjected to nat ural selection for epistasis resulting from genomic recombinations between different species. However, there is a severe shortage of relevant methodol ogies to estimate epistatic genetic effects and variances. A statistical mo del has recently been proposed to estimate the number of QTLs, their geneti c effects and allelic frequencies in segregating populations. This model is based on multiplicative gene action and derived from a two-level intra- an d interspecific mating design. In this paper, we formulate a statistical pr ocedure for partitioning the genetic variance into additive, dominant and v arious kinds of epistatic components in an intra- or mixed intra- and inter specific hybrid population. The procedure can be used to study the genetic architecture of fragmented populations and hybrid zones, thus allowing for a better recognition of the role of epistasis in evolution and hybrid speci ation. A real example for two Populus species, P. tremuloides and P. tremul a, is provided to illustrate the procedure. In this example, we found that considerable new genetic variation is formed through genomic recombination between two aspen species.