In its investigation of geographic structure within U.S. ethnic populations, this study analyzed 1,705 haplotypes on the basis of nine short tandem repeat (STR) loci on the Y-chromosome from 9 - 11 groups each of African-Americans, European-Americans, and Hispanics.
The study did not find any significant differences in the distribution of Y-STR haplotypes among African-American groups by geographic region. This was unexpected for two reasons. First, a large number of different African source populations contributed to current African-American groups, with approximately half coming from the area extending from Senegal to Western Nigeria, and the remaining half coming from the area extending from Eastern Nigeria in Angola. Second, the amount of admixture of African-Americans with European-Americans is thought to have varied across various geographic regions of the United States, with generally higher levels of admixture observed in Northern groups. European-American and Hispanic groups, on the other hand, did exhibit significant geographic heterogeneity. The significant heterogeneity, however, resulted from one sample. Removal of that sample in each case eliminated the significant heterogeneity. Multidimensional scaling analysis of Rst values showed that African-American groups constituted a distinct cluster; whereas, there was some intermingling of European-American and Hispanic groups. MtDNA data exist for many of these same groups. Estimates of the European-American genetic contribution to the African-American gene pool were 27.5 percent to 33.6 percent for the Y-STR haplotypes and 9 percent to 15.4 percent for the mtDNA types. The lack of significant geographic heterogeneity among Y-STR and mtDNA haplotypes in U.S. ethnic groups means that forensic DNA databases need not be constructed for separate geographic regions of the United States. This also means that regional variation in disease susceptibility within ethnic groups is more likely due to cultural/environmental factors than any genetic heterogeneity. 5 figures, 5 tables, and 47 references