Mapping QTL in outbred populations using selected samples

A simulation study was carried out to investigate the influence of family s election and selective genotyping within selected families on the power and bias of estimation of genetic parameters in an outbred population with a h alf-sib family structure. Marker genotypes were determined only for sires t hat had offspring in the high and low phenotypic tails of the entire distri bution of the trait of interest. Offspring of selected sires were genotyped . Within selected families, three different sampling schemes were considere d: 1) offspring sampled from the tails of the distribution; 2) offspring ra ndomly sampled; 3) all offspring of a. selected sire analyzed. Control data consisted of randomly sampled offspring from randomly chosen sires. An int erval mapping procedure based on the random model approach was applied to s imulated data. The QTL location and the variance components were estimated using the maximum likelihood technique. Compared with the control data, sel ective genotyping of sires increased power of QTL detection, but also resul ted in severely biased estimates for variance components, especially when t he most extreme offspring of selected sires were sampled. Including phenoty pic data from all individuals along with marker information obtained only o n selected offspring provided improved estimates of the QTL parameters with out loss in power. (C) Inra/Elsevier, Paris.