Linkage analysis based on identity-by-descent (IBD) allele-sharing can be used to identify a chromosomal region harboring a quantitative trait locus (QTL), but lacks the resolution required for gene identification. Consequently, linkage disequilibrium (association) analysis is often employed for fine-mapping. Fulker et al. [1] proposed a variance-components based combined linkage and association analysis for quantitative traits in sib pairs, in which association is modeled as a mean effect and linkage is modeled in the covariance structure. To control for spurious associations due to population stratification and admixture, genotype scores are decomposed into between-pairs (b) and within-pairs (w) components. The resulting fixed effect model for the mean phenotype is
