Random model approach for QTL mapping in half-sib families

An interval mapping procedure based on the random model approach was applied to investigate its appropriateness and robustness for QTL mapping in populations with prevailing half-sib family structures. Under a random model, QTL location and variance components were estimated using maximum likelihood techniques. The estimation of parameters was based on the sib-pair approach. The proportion of genes identical-by-descent (IBD) at the QTL was estimated from the IBD at two flanking marker loci. Estimates for QTL parameters (location and variance components) and power were obtained using simulated data, and varying the number of families, heritability of the trait, proportion of QTL variance, number of marker alleles and number of alleles at QTL. The most important factors influencing the estimates of QTL parameters and power were heritability of the trait and the proportion of genetic variance due to QTL. The number of QTL alleles neither influenced the estimates of QTL parameters nor the power of QTL detection. With a higher heritability, confounding between QTL and the polygenic component was observed. Given a sufficient number of families and informative polyallelic markers, the random model approach can detect a QTL that explains at least 15 % of the genetic variance with high power and provides accurate estimates of the QTL position. For fine QTL mapping and proper estimation of QTL variance, more sophisticated methods are, however, required. (C) Inra/Elsevier, Paris.