Gene frequency estimates for samples of Black and White twins from the Philadelphia metropolitan area.

Maximum likelihood estimates of gene frequencies and their standard errors are presented for 21 blood group and serum protein polymorphisms. The observed frequencies for certain high and low frequency antigens also are reported. The data come from a sample of 399 same-sex twin pairs and two sets of triplets from the Greater Philadelphia urban region encompassing roughly five counties in southeastern Pennsylvania and three counties of southern New Jersey. Analyses are carried out separately for the four subgroups created by subdividing the sample by race and co-twin. Total sample estimates are also calculated within the two socially defined racial groups. The gene frequency estimates generally appear to be consistent with previously reported data for U.S. urban populations. The frequency of the Fy allele in the Duffy system, however, seems to be the highest value thus far published for a white population. The white sample Fy allele very well may be a heterogeneous class in which only a very small fraction is comparable to the Fy allele common in the black sample.