POPULATION-GENETICS OF DINUCLEOTIDE (DC-DA)(N)CENTER-DOT(DG-DT)(N) POLYMORPHISMS IN WORLD POPULATIONS

We have characterized eight dinucleotide (dC-dA)(n).(dG-dT)(n) repeat loci located on human chromosome 13q in eight human populations and in a sample of chimpanzees. Even though there is substantial variation i n allele frequencies at each locus, at a given locus the most frequent alleles are shared by all human populations. The level of heterozygos ity is reduced in isolated or small populations, such as the Pehuenche Indians of Chile, the Dogrib of Canada, and the New Guinea highlander s. On the other hand, larger average heterozygosities are observed in large and cosmopolitan populations, such as the Sokoto population from Nigeria and German Caucasians. Conformity with Hardy-Weinberg equilib rium is generally observed at these loci, unless (a) a population is i solated or small or (b) the repeat motif of the locus is not perfect ( e.g., D13S197). Multilocus genotype probabilities at these microsatell ite loci do not show departure from the independence rule, unless the loci are closely linked. The allele size distributions at these (CA)(n ) loci do not follow a strict single-step stepwise-mutation model. How ever, this feature does not compromise the ability to detect populatio n affinities, when these loci are used simultaneously. The microsatell ite loci examined here are present and, with the exception of the locu s D13S197, are polymorphic in the chimpanzees, showing an overlapping distribution of allele sizes with those observed in human populations.