RATES OF CHANGE OF GENETIC-PARAMETERS OF BODY-WEIGHT IN SELECTED MOUSE LINES

A method based on the animal model is described which allows the estim ation of continuous changes in variance components over time using res tricted maximum likelihood (REML). The method was applied to the analy sis of a selection experiment in which a foundation population formed from a cross between two inbred strains of mice (C57BL/6J and DBA/2J) was divergently selected for 6 week body weight over 20 generations. T he analysis suggested that there was an increase in phenotypic varianc e of about 50% in the low selected lines over the course of the experi ment which was attributed to increases in the environmental and additi ve variance components. Variance changes in the High selected lines we re generally smaller than in the Low lines, although there was an esti mated 20% increase in the environmental variance. Simple models to exp lain these effects involving dominance, linkage and epistasis were exp lored. Testing which of these was responsible for the variance changes noted in this experiment (if any) is difficult, although the epistasi s and dominance models require less stringent conditions than the link age model, and the dominance model is supported by evidence of heteros is in the F-1.