A conditional model to estimate genetic parameters in data from a selected base population was investigated. The method assumes base parents as fixed and a conditional variance is based upon the Mendelian sampling of gametes from the base parents. In a simulation study, only sires were selected and mated to all females to create the next generation (2 progeny per female). Selection was for five generations but only animals of generations 4 and 5 were assumed to have performance records and parents known. Due to selection, initial genetic variance was underestimated when base animals from generation 3 were assumed random. However, when all base animals were assumed fixed, underestimation of genetic variance was even larger whereas the residual variance was overestimated. When males of generation 4 were not selected to have progeny, estimated variances were empirically unbiased. It was concluded that estimates for genetic parameters with the conditional model were not biased by selection of base animals, but a new bias was introduced when descendants of fixed base animals were selected to have progeny
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIII. Plenary lectures, molecular genetics and mapping, selection, prediction and estimation., , 476–479, 1990
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