Analysis of LD in the genome has made it clear that the correlations of genotypes are often so strong that one variant can fully predict (or “tag”) the genotype of another (perfect LD-see Figure 1), making it possible to examine all common variation by genotyping only a fraction of common SNPs. The HapMap project launched in 2002 (7) has genotyped millions of SNPs in multiple populations, achieving its goal to characterize LD across the genome. These results have already been utilized to enhance the efficiency of current genotyping technologies and they are a valuable everyday tool for complex disease genetics researchers.
