The Theory of Multiple Shifts

THE original suggestion that genetic gains from selection may be enhanced by the use of two or more shifts of males in the course of a breeding season was apparently made by Warren and Gish (1943). At least one group of investigators has adopted this notion with enthusiasm and has made specific recommendations for its use in commercial breeding practice (Hutt, 1949). Others have approached it more cautiously conceding that the scheme may have some value in family testing programs (Lerner, 1950). It is true that the proponents of the scheme allege success in application to a breeding program for resistance to lymphomatosis (Hutt and Cole, 1947), but their evidence is not based on controlled experimental comparisons. Neither has there been a theoretical evaluation of the potentialities of the multiple-shift scheme based on proper genetic models. Hence, in the absence of either a priori or a posteriori justification for adoption . . .