METHODS FOR MULTIPLE-MARKER MAPPING OF QUANTITATIVE TRAIT LOCI IN HALF-SIB POPULATIONS

In this paper we consider the detection of individual loci controlling quantitative traits of interest (quantitative trait loci or QTLs) in the large half-sib family structure found in some species. Two simple approaches using multiple markers are proposed, one using least square s and the other maximum likelihood. These methods are intended to prov ide a relatively fast screening of the entire genome to pinpoint regio ns of interest for further investigation. They are compared with a mor e traditional single-marker least-squares approach. The use of multipl e markers is shown to increase power and has the advantage of providin g an estimate for the location of the QTL. The maximum-likelihood and the least-squares approaches using multiple markers give similar power and estimates for the QTL location, although the likelihood approach also provides estimates of the QTL effect and sire heterozygote freque ncy. A number of assumptions have been made in order to make the likel ihood calculations feasible, however, and computationally it is still more demanding than the least-squares approach. The least-squares appr oach using multiple markers provides a fast method that can easily be extended to include additional effects.