in the region are listed. The length of the line reflects the length of the gene. One will note that the Taq1A allele is actually located in a small gene next to DRD2 called ANKK1. It is not located in DRD2 despite the large literature making claims about whether DRD2 was involved in many different phenotypes of interest based on genotyping at this marker. Below the genes is the LD plot, where shading indicates the degree of correlation between markers (shown here as the small hash marks at the top of the figure) as measured by D′ (Hedrick & Kumar 2001), with darker red shading indicating higher correlations; blue or white shading indicates the markers are unlinked or uncorrelated. What stands out is the block-like correlational structure, yielding inverted red triangles that indicate groups of SNPs where there is high LD across that group of SNPs and low LD with surrounding SNPs located outside the block. This block-like structure is observed throughout the genome (Gabriel et al. 2002). Knowing the correlation pattern is critical for the selection of markers and the interpretation of genetic association results. For example, DRD2 spans at least two blocks on the figure. If different studies
