RESUMEN
Several new HLA-B locus alleles have been discovered in South American Amerindians. By contrast, analysis of the MHC class I alleles of North American native populations has revealed few new HLA-B alleles. This suggests that the HLA-B locus is evolving rapidly in South American populations. Here we describe the HLA-B locus alleles present in individuals from a Central American tribe, the Kuna of Panama. Using a sequence-based typing technique that separates alleles by denaturing gradient gel electrophoresis (DGGE) followed by direct sequencing, we determined the HLA-B alleles from eight Kunas. Two of the HLA-B alleles present in the Kuna have been previously described in other South American Amerindian populations; one allele has been characterized in a Mexican-American. We characterized two new HLA-B alleles in the Kuna, HLA-B*3911 and HLA-B*5110. HLA-B*3911 differed from HLA-B*3905 by only a single nucleotide substitution in exon 3. This substitution resulted in an amino acid replacement of leucine by arginine at residue 156 in the alpha 2 domain. Such a change may affect the repertoire of peptides that are bound by this molecule. HLA-B*5110 differed significantly from other HLA-B*51 alleles in that it is the result of an unusually large intra-locus recombination event of minimally 216 nucleotides. This recombination results in an allele that is part HLA-B*51 and part HLA-B*40. Thus, more dramatic recombination events may also play a role in the rapid evolution of the HLA-B locus in Amerindians.
Asunto(s)
Antígenos HLA-B/genética , Indígenas Centroamericanos/genética , Alelos , Secuencia de Aminoácidos , Secuencia de Bases , Antígeno HLA-B39 , Antígeno HLA-B51 , Humanos , Datos de Secuencia Molecular , PanamáRESUMEN
Mitochondrial and nuclear DNA diversities were determined for two Chocó-speaking Amerind populations, the Emberá and Wounan, sampled widely across their geographic range in eastern Panamá. These data were compared with mitochondrial and nuclear diversities determined here and previously for neighboring Chibcha-speaking Ngöbé and Kuna populations. Chocoan groups exhibited mitochondrial diversity levels typical for Amerind populations while Chibchan groups revealed reduced mitochondrial diversity. A slight reduction in autosomal levels of heterozygosity was determined for the Chibcha while X and Y variation appeared equivalent in all populations. Genetic distinctiveness of the two linguistic groups contradicts the anthropological theory that Paleoindians migrated repeatedly through the isthmian region and, instead, supports the idea of cultural adaptation by endogenous populations. Reduced genetic diversity in Chibchan populations has been proposed to represent a population bottleneck dating to Chibchan ethnogenesis. The relative sensitivities of haplotype pairwise difference distributions and Tajima's D to detect demographic events such as population bottlenecks are examined. Also, the potential impact of substitution rate heterogeneity, population subdivision, and genetic selection on pairwise difference distributions are discussed. Evidence is presented suggesting that a larger effective population size may obscure the historical signal obtained from nuclear genes while the single mitochondrial locus may provide a moderately strong signal.
Asunto(s)
ADN Mitocondrial , ADN , Variación Genética , Indígenas Centroamericanos/genética , Núcleo Celular , Humanos , Cómputos Matemáticos , Panamá/etnología , Filogenia , Polimorfismo de Longitud del Fragmento de Restricción , Análisis de Secuencia de ADNRESUMEN
Mitochondrial DNA (mtDNA) haplotype diversity was determined for 46 Ngöbé Amerinds sampled widely across their geographic range in western Panamá. The Ngöbé data were compared with mtDNA control region I sequences from two additional Amerind groups located at the northern and southern extremes of Amerind distribution, the Nuu-Chah-Nulth of the Pacific Northwest and the Chilean Mapuche and from one Na-Dene group, the Haida of the Pacific Northwest. The Ngöbé exhibit the lowest mtDNA control region sequence diversity yet reported for an Amerind group. Moreover, they carry only two of the four Amerind founding lineages first described by Wallace and coworkers. We posit that the Ngöbé passed through a population bottleneck caused by ethnogenesis from a small founding population and/or European conquest and colonization. Dating of the Ngöbé population expansion using the Harpending et al. approach to the analysis of pairwise genetic differences indicates a Ngöbé expansion at roughly 6800 years before present (range: 1850-14,000 years before present), a date more consistent with a bottleneck at Chibcha ethnogenesis than a conquest-based event.
Asunto(s)
ADN Mitocondrial/genética , Variación Genética , Indígenas Centroamericanos/genética , Arqueología , Secuencia de Bases , Femenino , Haplotipos/genética , Humanos , Masculino , Datos de Secuencia Molecular , Panamá , Filogenia , Polimorfismo de Longitud del Fragmento de Restricción , Alineación de SecuenciaRESUMEN
Mitochondrial DNA (mtDNA) haplotype diversity was determined for 63 Chibcha-speaking Kuna Amerinds sampled widely across their geographic range in eastern Panamá. The Kuna data were compared with mtDNA control region I sequences from two neighboring Chibchan groups, the Ngöbé and the Huetar; two Amerind groups located at the northern and southern extremes of Amerind distribution, the Nuu-Chah-Nulth of the Pacific Northwest and the Chilean Mapuche; and with a single Na-Dene group, the Haida of the Pacific Northwest. The Kuna exhibited low levels of mitochondrial diversity as had been reported for the other two Chibchan groups and, furthermore, carried only two of the four Amerind founding lineages first reported by Schurr and coworkers (Am. J. Hum. Genet. 1990; 46: 613-623). We posit that speakers of modern Chibchan languages (henceforth referred to as the Chibcha) passed through a population bottleneck caused either by ethnogenesis from a small founding population and/or subsequent European conquest and colonization. Using the approach of Harpending et al. (Curr. Anthropol. 1993; 34: 483-496), we estimated a Chibchan population bottleneck and subsequent expansion approximately 10,000 years before present, a date consistent with a bottleneck at the time of Chibchan ethnogenesis. The low mtDNA diversity of Kuna Amerinds, as opposed to the generally high levels of mtDNA variation detected in other Amerind groups, demonstrates the need for adequate sampling of cultural or racial groups when attempting to genetically characterize human populations.