Formula for estimating pathway effects (aij) based on QTL additive and epistatic effects (A) and their corresponding portions in the total genotypic variance, in an ideal F2 (under complete dominance at all segregating loci) or RI (DH) population.

is the expected genotypic variance for trait X in the population. In an F2, the QTL epistatic effects, , , and represent 1st, 2nd and 3rd order additive by additive epistasis parameters, respectively; % of is the proportion of the total genotypic variation explained by , , , and , respectively. p and q are allelic frequencies of the two alleles at each locus involved, which is 0.5 in the ideal F2 and RI (DH) populations.