METHODS OF SEGREGATION ANALYSIS FOR ANIMAL BREEDING DATA - PARAMETER ESTIMATES

Three approximations to the combined model likelihood (including varia tion due to both polygenes and a major gene) used in segregation analy sis were compared in their ability to estimate the parameters describi ng the model. Paternal half-sib data simulated under four different co mbined models were used. In general, when a combined model provides th e best explanation of the data the parameter estimates from all three approximations investigated are, on average, in good agreement with th e values simulated. The use of Hermite integration to replace the inte gration in the combined model likelihood provided the parameter estima tes closest to those simulated. The other two approximations, based on extensions of linear mixed-model theory, gave estimates further from the expected values, however, these latter two methods can estimate tr ansmitting abilities for the sires directly from the analyses. The thr ee approximations are similar in their ability to genotype sires at th e major locus. On average, with the models studied here, about 65 per cent of sires can be successfully genotyped.