Our results also suggests the potential for further definition of more homogeneous population groups for genetic studies that may theoretically decrease both type 1 and type 2 error rates. Geneticists have long recognized that different population groups may provide enhanced opportunities to uncover susceptibility loci based on more limited genetic heterogeneity. For complex genetic diseases some specific studies may focus on particular population groups to enhance the power to find important gene variants. For example, the study of Crohn's disease [#266600] in Ashkenazi Jewish individuals has the advantage of examining a potentially more homogeneous population with a higher frequency of this particular disease than in a mixed European population. This approach is supported by our results suggesting that a very large proportion of this particular ethnic group can be distinguished by analysis of substructure. Moreover, our results provide the ability to further define and restrict this study population by allowing the identification and exclusion of subgroup outliers in association tests in studies of complex genetics in Ashkenazi Jewish populations. In addition, pre-genotyping of potential cases and controls with as few
