POINT ESTIMATION AND GRAPHICAL INFERENCE OF MARGINAL DOMINANCE FOR 2 VIABILITY LOCI CONTROLLING INBREEDING DEPRESSION

A deterministic analysis is conducted to examine marginal dominance fo r two linked viability loci influencing inbreeding depression and its graphical inferences. Four estimators of marginal dominance are derive d, assuming a biallelic marker locus completely linked to one of the v iability loci, and the biases in expected estimates due to the other d eleterious locus are discussed. Three conditions under which apparent partial dominance or underdominance could occur are found, i.e. when t wo multiplicative, partially recessive loci are linked in coupling pha se and when two synergistic, highly overdominant loci are linked in co upling or repulsion phases. Expected frequencies of the three marker g enotypes in selfed progeny are derived, considering two linkage phases , two types of marker locus position with respect to the viability loc i, and the multiplicative and synergistic fitness models. Segregation ratios are generated for the marker locus linked to either two overdom inant or partially recessive loci and plotted in gene action graphs to examine the robustness of the graphical inferences of gene action due to the presence of an additional linked viability locus. Under a mult iplicative fitness model, the presence of an additional partially rece ssive or overdominant locus in the vicinity of the marker locus does n ot greatly affect the graphical inferences of the relative role of par tially recessive or overdominant genes in expression of inbreeding dep ression. A marker linked to two synergistic, highly overdominant loci can behave as though linked to a partially recessive, partially domina nt or underdominant locus, even with relatively weak synergism.