Pedigree-wide regression analyses were conducted for the 22 autosomal chromosomes using MERLIN-REGRESS version 1.1.2 (Abecasis et al., 2002). The method, an extension of the Haseman-Elston procedure (Haseman and Elston, 1972), implements a regression-based process for linkage analysis using trait-squared sums and differences to predict identity-by-descent (IBD) sharing between any non-inbred relative pairs (Sham et al., 2002). For allelic regions containing influential genes, greater phenotype similarity (i.e. smaller squared trait differences) is expected for relative pairs with more alleles in common. MINX (Abecasis et al., 2002) was used to examine linkage for the X chromosome.
