Relationships between genetic distance and dominance and epistatic effects in line-crosses of mice

From each of two populations, the outbred NMRI(N) and the synthetic four-way cross (S), a line was selected for high 8-week body weight (N8,S8), one for low 8-week body weight (N6, S6) and one line served as control (N9, S9). One N line was selected for an antagonistic goal, high 3-5 week gain and low 8-week body weight. After 54 generations of selection lines were crossed and F1, F2 and backcrosses produced. From these the genetic effects, additive, dominance, additive × additive (axa) and (additive × dominance) (axd) epistatic, were estimated. Based on the frequencies of nine biochemical markers, genetic distances as proposed by Cavalli-Sforza and Nei were estimated between the lines. Dominance and epistatic effects increased with distance. Adding a quadratic term raised the statistical significance of distance on axa effects to near 0.10. When the marker distance was supplemented with a distance caused by selection the statistical significance of the predictor for axa of both 5-8 week gain and BW8 passed 0.05.