Selection for Body Weight at Eight Weeks of Age

CORRELATED responses of unselected traits may result from genetic effects, environmental influences and a combination of the two. The phenotypic correlation (rP) which is the association between two traits that can be observed directly, can be partitioned into two fractions, namely genetic (rG) and environmental (rE). The former is the additive genetic component of the covariance while the latter includes the remainder of the covariance which includes non-additive genetic and environmental covariance. The relationship between the correlations may be expressed as: rp = rG hx hy + rE ex ey where, ex and ey are the square roots of l-h2x and l-h2y, respectively. Although many estimates of genetic, phenotypic and environmental correlations have been reported, information on time trends of correlations during a selection experiment is meager. The present report contains the time trends of phenotypic, genetic and environmental correlations between the selected trait, eight-week body weight, and unselected traits …