1. Supplementary Figure Legends Supplementary Figure 1: The variance of pD  H activity plotted against mean pD  H activity for three populations, obtained from the table published in Zabetian et al (2001). For each population, the blue profile is the genotype-specific variance vs. the mean of pD  H activity at rs1611115, the red straight line connects the estimated mean for the high homozygote and the origin and the vertical lines are the 95% confidence intervals for the observed variances on the assumption of normal distributions. Supplementary figure 2: Model-based linkage analysis of pDβH activity on chromosome 19. The red solid- line profile is the multi-point linkage for pD  H activity, with Mendelian additive model under logarithm transformation. The blue dotted-line profile is the multi-point linkage for the new trait (after adjusting for 25 SNPs on chromosome 9), with new Mendelian dominant model under logarithm transformation. Supplementary figure 3: Model-free linkage analysis of pDβH activity on chromosome 19. The red solid- line profile is the linkage for pD  H activity under logarithm transformation. The blue dotted-line profile is the linkage for the new trait (after adjusting for 25 SNPs on chromosome 9), under logarithm transformation. Supplementary figure 4: Genome-wide model-based linkage of the new trait formed by adjusting for the 25 SNPs, with an additive model under the square-root transformation.

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5. Supplemental Figure 4