ALPHA-GLOBIN GENE HAPLOTYPES IN SOUTH-AMERICAN INDIANS

The haplotypes of the alpha-globin gene cluster were determined for 99 Indians from the Brazilian Amazon region who belong to 5 tribes: Waya mpi, Wayana-Apalai, Kayapo, Arara, and Yanomami. Three predominant hap lotypes were identified: Ia (present in 38.9% of chromosomes), IIIa (2 5.8%), and IIe (22.1%). The only alpha-globin gene rearrangement detec ted was alpha alpha alpha(3.7) I gene triplication associated with hap lotype IIIa, found in high frequencies (5.6% and 10.6%) in two tribes and absent in the others. alpha-Globin gene deletions that cause alpha -thalassemia were not seen, supporting the argument that malaria was a bsent in these populations until recently. The heterogeneous distribut ion of alpha-globin gene haplotypes and rearrangements among the diffe rent tribes differs markedly from the homogeneous distribution of beta -globin gene cluster haplotypes and reflects the action of various gen etic mechanisms (genetic drift, founder effect, consanguinity) on smal l isolated population groups with a complicated history of divergence- fusion events. The alpha-globin gene haplotype distribution has some s imilarities to distributions observed in Southeast Asian and Pacific I sland populations, indicating that these populations have considerable genetic affinities. However, the absence of several features of the a lpha-globin gene cluster that are consistently present among the Pacif ic Islanders suggests that the similarity of haplotypes between Brazil ian Indians and people from Polynesia, Micronesia, and Melanesia is mo re likely the result of ancient common ancestry rather than the conseq uence of recent direct genetic contribution through immigration.