GENETIC EVALUATION FOR A QUANTITATIVE TRAIT CONTROLLED BY POLYGENES AND A MAJOR LOCUS WITH GENOTYPES NOT OR ONLY PARTLY KNOWN

For a quantitative trait controlled by polygenes and a major locus wit h 2 alleles, equations for the maximum likelihood estimation of major locus genotype effects and polygenic breeding values, as well as major allele frequency and major locus genotype probabilities, were derived . Because the resulting expressions are computationally untractable fo r practical application, possible approximations were compared with 2 other procedures suggested in the literature using stochastic computer simulation. Although the frequency of the favourable allele was serio usly underestimated when major locus genotypes were entirely unknown, the proposed method compares favourably with the 2 other procedures un der certain conditions. None of the procedures compared can satisfacto rily separate major genotypic effects from polygenic effects. However, the proposed method has some potential for improvement.