Formula for estimating pathway effects (<i>a_ij</i>) based on QTL additive and epistatic effects (<i>A</i>) 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.