Joint genetic evaluation of purebred and crossbred data under dominance

Currently available software packages are not able to handle the joint gene tic evaluation of pure and crossbred data correctly. Instead, the same trai ts originating in the two purebreds and the crossbred are treated as three separate traits and analysed in a three trait animal model. Using selection index theory it can be demonstrated that this procedure contains model vio lations even if only additive genetic effects are considered. The effective ness of the correct model which allows different contributions of the paren tal lines to the genetic variance of the cross including animal specific do minance effects is assessed on the basis of different selection indices. Th e sources of information chosen reflect those available in typical chicken breeding programs. The genetic parameters required for index construction - in particular the dominance variance and the genetic correlation between t he pure and cross breds - were derived using a two locus model. If the pure bred contribute extremely differently to the crossbred variance large losse s in efficiency can be observed. With contributions of the sire line of 11, 19, 37 and 40% to the additive genetic variance of the cross corresponding losses in efficiency of selection where 13.1, 6.5, 0.6 and 0.2% respective ly. Not considering the dominance variance - depending on its proportion re lative to the total genetic variance - lead to a moderate loss of efficienc y from 0.1 to 2.6%.