Loci Differentially Affected by Selection in Two American Black Populations

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Abstract
The hypothesis that loci differentially affected by selection can be identified was tested by a comparison of two American black populations. The hypothesis had previously been studied in Evans County, Georgia and the data from that study were compared with data obtained from the population of Sapelo Island, Georgia. In both, gene frequencies for 21 polymorphic systems were determined. Estimates were made for 14 of these traits of the gene migration (m) from whites into these black populations, by use of the equation: m = (q(n) - q(Af))/(q(w) - q(Af)), where q(w), q(n), and q(Af) are the frequencies of an allele in the white, black, and West African populations, respectively. In this calculation, it is assumed that the differences in gene frequencies between American blacks and Africans are due entirely to gene mixture. On this assumption, if only gene mixture were operating, the values of "m" determined for each locus would be about the same. If "m" has a different value at some loci than it has at others, then selection for traits controlled by genes segregating at these loci could account for this difference. Values of "m" in both populations were scattered. These values were ranked for each population and the rank orders compared. There was a highly significant association between the rank order of loci in the two populations. This finding supports the hypothesis that loci differentially affected by selection can be identified, and that the selective forces have operated on the same loci in both populations.