The validity of genetic models underlying quantitative traits

This paper reviews the validity of the assumptions and predictions of genetic models used for the analysis of quantitative traits. When data on phenotypes and pedigrees but not individual genes are available, the traditional, additive, infinitesimal model makes satisfactory predictions of short-term response to selection despite the incorrectness of its assumptions. Improvements can made in the model such as the inclusion of non-additive variance components or major genes but gains in the accuracy of prediction have seldom been demonstrated. When data are available on individual genes or markers, two models are in common use - a two allele and an infinite allele model. The two models differ in a number of respects such as assumptions about segregation variance, estimation of fixed or random effects and number of parameters to be estimated when multiple traits are used. There is little information on the accuracy with which either model predicts the performance of future animals. (C) 2001 Elsevier Science B.V. All rights reserved.