On estimating non-additive genetic parameters in chickens

Several economically important traits in two Leghorn populations (over 9000 birds) were examined for additive and non-additive components of genetic variance and sex-linked effects. Data were analysed by two different statistical models based on least-squares procedures. 2. Six different covariances were first calculated between relatives; i.e., full-sibs 3/4-sisters, half-sisters, dam-daughters, grandam-granddaughters and aunt-nieces. 3. From the covariances, weighted least-squares equations were used to obtain estimates of variance components for additive genetic, dominance, maternal and sex-linkage effects. 4. The estimates of non-additive components were highly variable but generally small compared with the additive genetic estimates. 5. In general this study suggests that for most traits, with the possible exception of rate of egg production, there is relatively little non-additive genetic variation. 6. The consequences of possible negative correlations between additive effects and maternal effects are considered as they might apply to egg production in poultry.