Differences in total effects of the three loci Growth4, Growth9.1, and Growth 12 based on their context.

The rows show the effect of the triplet when increasing numbers of loci are taken into account. The first row (k = 1; only the primary locus) gives the summation of the marginal effects of the three loci. The second row (k = 2; primary locus with one background locus) gives the effect the loci calculated as the average over the two pairs that it is part of (each locus is assumed to contribute half the effect of the pair). The third row (k = 3; all three loci together) gives the effect for each locus is a third of the entire triplet effect. As can be seen, using either k = 1 or k = 2 leads to underestimation of the total impact of the three loci.