No abstract

Ten-level synthetic gene frequency maps derived from a principal component analysis of seven polymorphic loci are displayed for a large sample of North Amerindian populations. These maps are useful for assessing population affinities over broad geographical regions and perhaps, as others have argued, for inferring recent migrations. The influence of European admixture is investigated by deleting highly admixed populations and regenerating the maps. In broad outline the resultant geographic patterning, while appearing more homogeneous, preserves many features of the maps that include the highly admixed samples--especially with respect to the Eskimo/non-Eskimo dichotomy. Further, in an effort to evaluate how varying the number of display levels affects patterning as well as interpretation, the maps were replotted at 5 and 20 levels. The 5-level maps are found to accentuate differences between the full data set and the less admixed data set, while the 20-level maps tend to obscure these differences.

A survey of nine polymorphic loci for 82 North Amerindian populations was undertaken to test the hypothesis that increasing levels of sociocultural complexity are ineluctably accompanied by increased heterozygosity. The data reveal a significant relationship in the predicted direction. Moreover, the significant correlation between average heterozygosity and sociocultural complexity is substantially increased by the removal of 19 highly admixed samples. However, this relationship, at least among North Amerindian populations, may be more apparent than real since both mean heterozygosity and the level of sociocultural organization are significantly negatively correlated with latitude. When this latter variable is controlled for, all correlations between heterozygosity and sociocultural complexity are rendered nonsignificant.

For an arbitrary number of affected sibs with unaffected parents, the proportion that share both marker haplotypes identical by descent is derived for the generalized single locus model. This proportion is shown to depend on the underlying parameters of the disease transmission model, on the total sibship size and on the number of sibs who are affected. The variety of identity by descent patterns suggests that any attempt to infer the presence of other independent disease susceptibility loci solely on the basis of an observed inverse relationship between the degree of haplotype sharing and the number of affected sibs, is liable to result in spurious conclusions.

Allelic frequencies at seven polymorphic loci in 74 North Amerindian populations are examined relative to patterns of climatic variation. Canonical correlation analysis reveals strong and significant associations of heterozygosity at the ABO, Ss, Duffy, and P loci with climatic variability. Principal component analysis demonstrates that these loci tend to form correlated ensembles. Moreover, canonical correlation analysis of component scores provides support for an association between polymorphism at these loci and environmental variability. The results are concordant with two previous investigations which suggested a relationship between polymorphism for the ABO, Duffy, and Diego systems and climate. It is suggested that the examination of broad geographic patterns of genetic variation at multiple loci is a valuable, but underutilized, method of screening for the effects of long-term systematic pressures.