Selection for Breast Angle at Eight Weeks of Age

IN SINGLE trait selection experiments correlated responses are the simultaneous changes in unselected traits which result from selection for one particular characteristic. The association between selected and unselected traits is due to genetic effects, environmental influences and a combination of both. The genetic effects are caused by pleiotropy and linkage. Pleiotropy results in more permanent genetic associations while those caused by linkage are likely to be transient (Falconer, 1960). Although genetic and environmental correlations between two traits may be estimated from information on relatives by techniques presented by Hazel (1943) and Hazel et al. (1943), it is of value to measure the actual changes which occur in one trait when individual selection is for another characteristic. This is because selection experiments yield realized genetic and environmental correlations. Also of considerable interest is information on the consistency of the magnitude of the associated responses when selection is practiced for several generations.…