REALIZED SAMPLING VARIANCES OF ESTIMATES OF GENETIC-PARAMETERS AND THE DIFFERENCE BETWEEN GENETIC AND PHENOTYPIC CORRELATIONS

A data set of 1572 heritability estimates and 1015 pairs of genetic an d phenotypic correlation estimates, constructed from a survey of publi shed beef cattle genetic parameter estimates, provided a rare opportun ity to study realized sampling variances of genetic parameter estimate s. The distribution of both heritability estimates and genetic correla tion estimates, when plotted against estimated accuracy, was consisten t with random error variance being some three times the sampling varia nce predicted from standard formulae. This result was consistent with the observation that the variance of estimates of heritabilities and g enetic correlations between populations were about four times the pred icted sampling variance, suggesting few real differences in genetic pa rameters between populations. Except where there was a strong biologic al or statistical expectation of a difference, there was little eviden ce for differences between genetic and phenotypic correlations for mos t trait combinations or for differences in genetic correlations betwee n populations. These results suggest that, even for controlled populat ions, estimating genetic parameters specific to a given population is less useful than commonly believed. A serendipitous discovery was that , in the standard formula for theoretical standard error of a genetic correlation estimate, the heritabilities refer to the estimated values and not, as seems generally assumed, the true population values.