Various notations and parameterizations may be found in the literature. The notation used here has enjoyed widespread application for the analysis of digenic effects on the means and variances of generations derived from crosses between inbred lines of diploid species and for specifying the components of genetic variance in randomly mating populations (Mather 1974). The model specifies the homozygous (additive effects) and heterozygous effects (dominance effects) of the two loci, da, db, ha and hb respectively, and the four possible types of epistatic interaction between them: between homozygotes, iab; between homozygotes at the A/a locus (AA versus aa) and heterozygote at B/b, jab; between heterozygote at the A/a locus and homozygote at B/b, jba; between both heterozygous effects, lab. While the notation appears cumbersome, it has the advantage of generality in capturing characteristic patterns of classical epistatic segregation in Mendelian dihybrid crosses while not being restricted by them. The classical patterns of epistasis were described in the first decade of the 20th century (see e.g. Miko 2008, for a recent didactic summary of the classical ratios). Thus, the 9:7 F2
