A 2-STAGE HALF-SIB DESIGN FOR MAPPING QUANTITATIVE TRAIT LOCI IN FOODANIMALS

Daughter and granddaughter half-sib designs for mapping quantitative t rait loci were modified to increase experimental power. This new desig n includes a two-stage procedure, in contrast to conventional one-step half-sib designs. In stage 1, a few progeny of each sire are genotype d for marker loci. Based on the analyses of stage 1 data, some sires a re chosen to continue genotyping more progeny for stage 2. When multip le chromosomes are under investigation, chromosomes and sires for stag e 2 are selected based on the analysis of stage 1 data. Sire selection results in increased frequency of heterozygous genotypes of interest in stage 2 if the markers are linked to those genes. Chromosome select ion can increase the proportion of chromosomes with segregating quanti tative trait loci in stage 2 if not all of the chromosomes evaluated i n stage 1 have segregating quantitative trait loci. Numerical results indicated that two-stage half-sib designs are generally more powerful than conventional designs when 1) the noncentrality parameter is moder ate or larger, 2) larger quantitative trait loci are mapped using tigh tly linked markers in larger families, and 3) variation is large in nu mbers and sizes of segregating quantitative trait loci among the chrom osomes evaluated in stage 1.