Non-Additive Gene Effects of Six Broiler Traits as Studied from a Series of Diallel Matings ,

Abstract

GENERALLY, the discrepancy between the observed and the expected genetic changes under selection is sufficiently small to be attributed to errors in sampling. In those cases where the observed deviates excessively from the expected, theories for such a departure must be invoked to reconcile it to the general framework of population genetics. It has been the experience of breeders that response to selection in highly selected populations frequently falls short of that expected on theoretical grounds. Furthermore, several investigators observed a cessation of genetic changes in their long-term selection experiments (Mather and Harrison, 1949; Lerner and Dempster, 1951; Woodworth et al., 1952; Robertson and Reeve, 1952; Falconer and King, 1953; and Yamada et al., 1958). Various theories have been advanced to interpret such lack of response to selection, all of which can be classified into three categories:(1) The exhaustion of genetic variability as a result of selection and inbreeding.