POWER OF 2-GENERATION AND 3-GENERATION QTL MAPPING EXPERIMENTS IN AN OUTBRED POPULATION CONTAINING FULL-SIB OR HALF-SIB FAMILIES

QTL mapping experiments involve many animals to be genotyped and perfo rmance tested. Consequently, experimental designs need to be optimized to minimize the costs of data collection and genotyping. The present study has analyzed the power and efficiency of experiments with two- o r three-generation family structures containing full-sib families, hal f-sib families, or both. The focus was on data from one outbred popula tion because the main interest is to locate genes that can be used for within-line selection. For a two-generation experiment more animals h ad to be typed for marker loci to obtain a certain power than for a th ree-generation experiment. Fewer trait values, however, had to be obta ined for a two-generation experiment than for a three-generation exper iment. A two- or three-generation family structure with full-sib offsp ring was more efficient than a two- or three-generation family structu re with half-sib offspring. A family structure with full-sib grand-off spring, however, was less efficient than a family structure with half- sib grand-offspring. For the most-efficient family structure each pair of parents had full-sib offspring that were genotyped for the marker. For the most-efficient family structure each full-sib offspring had h alf-sib grand-offspring for which trait values were obtained. For equa l power with a heritability of 0.1 and 100 grand-offspring per full-si b offspring, 30-times less marker typings were required for this most efficient family structure than for a two-generation half-sib structur e in which marker genotypes and trait values were obtained for half-si b offspring. The effect of heritability and the type of analysis (sing le marker or interval analysis) on the efficiency of a family structur e is described. The results of this study should help to design QTL ma pping experiments in an outbred population.