Genetic admixture, relatedness, and structure patterns among Mexican populations revealed by the Y-chromosome.

Y-linked markers are suitable loci to analyze genetic diversity of human populations, offering knowledge of medical, forensic, and anthropological interest. In a population sample of 206 Mestizo males from western Mexico, we analyzed two binary loci (M3 and YAP) and six Y-STRs, adding to the analysis data of Mexican Mestizos and Amerindians, and relevant worldwide populations. The paternal ancestry estimated in western Mexican-Mestizos was mainly European (60-64%), followed by Amerindian (25-21%), and African ( approximately 15%). Significant genetic heterogeneity was established between Mestizos from western (Jalisco State) and northern Mexico (Chihuahua State) compared with Mexicans from the center of the Mexican Republic (Mexico City), this attributable to higher European ancestry in western and northern than in central and southeast populations, where higher Amerindian ancestry was inferred. This genetic structure has important implications for medical and forensic purposes. Two different Pre-Hispanic evolutionary processes were evident. In Mesoamerican region, populations presented higher migration rate (N(m) = 24.76), promoting genetic homogeneity. Conversely, isolated groups from the mountains and canyons of the Western and Northern Sierra Madre (Huichols and Tarahumaras, respectively) presented a lower migration rate (N(m) = 10.27) and stronger genetic differentiation processes (founder effect and/or genetic drift), constituting a Pre-Hispanic population substructure. Additionally, Tarahumaras presented a higher frequency of Y-chromosomes without Q3 that was explained by paternal European admixture (15%) and, more interestingly, by a distinctive Native-American ancestry. In Purepechas, a special admixture process involving preferential integration of non-Purepecha women in their communities could explain contrary genetic evidences (autosomal vs. Y-chromosome) for this tribe.

Forensic potential of the STR DXYS156 in Mexican populations: inference of X-linked allele null.

The pentanucleotide STR (TAAAA)n DXYS156 offers advantages for genetic identity testing. In addition to establish the gender, DXYS156 expands the DNA profile and is able to indicate the possible geographic origin of the individual. We analyzed DXYS156 in 757 individuals of both sexes from Mexican populations. We studied the cosmopolitan Mestizo population and six Mexican ethnic groups: Tarahumaras, Purépechas, Nahuas, Mayas, Huicholes and Mezcala Indians. The six shorter (4-10) and the three larger alleles (11-13) were specific for the X and Y-chromosomes, respectively. A random distribution of alleles into genotypes was observed in males and females from each population. We estimated the power of exclusion for paternity testing according to the son's gender, and the power of discrimination in forensic casework. In addition, we detected a relatively high frequency of an X-linked allele null, principally in Mexican-Mestizos (3.6%), which must be considered when DXYS156 be applied for identification purposes.

Y-linked haplotypes in Amerindian chromosomes from Mexican populations: genetic evidence to the dual origin of the Huichol tribe.

We studied six Y-linked short tandem repeats (Y-STRs) to describe the internal diversity of the Amerindian haplogroup Q-M3 in 129 males from eight Mexican populations. The low gene diversity in the Huichol tribe demonstrated the effects of genetic drift, attributable to geographic isolation and founder effect. The presence of two principal paternal lineages supported the historical and anthropometric records, which indicate that Huichols were formed by the fusion of two ancestral Mexican tribes. Moreover, genetic distances and close relationships of haplotypes between Huichols and Tarahumaras were in agreement with their linguistic affiliation. The high genetic diversity of the Purépechas and wide distribution of haplotypes along the constructed network-joining tree suggest that the present genetic composition was influenced by Purépecha dominance in western Mesoamerica. The Y-haplotypes shared between populations suggest that, among the Amerindian tribes studied herein, the paternal genetic pool of Nahuas could have contributed more importantly to the European-admixed population, the Mexican-Mestizos.

Population data of nine STRs of Mexican-Mestizos from Mexico City.

One hundred and thirteen individuals were PCR-typed for nine STR loci with the AmpFlSTR Profiler Plus PCR amplification kit, including the following autosomal STRs: D3S1358, vWA, FGA, D8S1179, D21S11, D18S51, D5S818, D13S317 and D7S820. Allele frequencies for each STR were estimated, and they were compared to other populations. Genotype distribution by locus and by two-loci combination was in agreement with Hardy-Weinberg expectations for all nine STRs. For this region of Mexico, the combined probability of exclusion (PE) and power of discrimination (PD) were estimated: PE=99.964% and PD>99.999%.