Evaluating the Farming/Language Dispersal Hypothesis with genetic variation exhibited by populations in the Southwest and Mesoamerica.

The Farming/Language Dispersal Hypothesis posits that prehistoric population expansions, precipitated by the innovation or early adoption of agriculture, played an important role in the uneven distribution of language families recorded across the world. In this case, the most widely spread language families today came to be distributed at the expense of those that have more restricted distributions. In the Americas, Uto-Aztecan is one such language family that may have been spread across Mesoamerica and the American Southwest by ancient farmers. We evaluated this hypothesis with a large-scale study of mitochondrial DNA (mtDNA) and Y-chromosomal DNA variation in indigenous populations from these regions. Partial correlation coefficients, determined with Mantel tests, show that Y-chromosome variation in indigenous populations from the American Southwest and Mesoamerica correlates significantly with linguistic distances (r = 0.33-0.384; P < 0.02), whereas mtDNA diversity correlates significantly with only geographic distance (r = 0.619; P = 0.002). The lack of correlation between mtDNA and Y-chromosome diversity is consistent with differing population histories of males and females in these regions. Although unlikely, if groups of Uto-Aztecan speakers were responsible for the northward spread of agriculture and their languages from Mesoamerica to the Southwest, this migration was possibly biased to males. However, a recent in situ population expansion within the American Southwest (2,105 years before present; 99.5% confidence interval = 1,273-3,773 YBP), one that probably followed the introduction and intensification of maize agriculture in the region, may have blurred ancient mtDNA patterns, which might otherwise have revealed a closer genetic relationship between females in the Southwest and Mesoamerica.

Y-chromosome diversity in Native Mexicans reveals continental transition of genetic structure in the Americas.

The genetic characterization of Native Mexicans is important to understand multiethnic based features influencing the medical genetics of present Mexican populations, as well as to the reconstruct the peopling of the Americas. We describe the Y-chromosome genetic diversity of 197 Native Mexicans from 11 populations and 1,044 individuals from 44 Native American populations after combining with publicly available data. We found extensive heterogeneity among Native Mexican populations and ample segregation of Q-M242* (46%) and Q-M3 (54%) haplogroups within Mexico. The northernmost sampled populations falling outside Mesoamerica (Pima and Tarahumara) showed a clear differentiation with respect to the other populations, which is in agreement with previous results from mtDNA lineages. However, our results point toward a complex genetic makeup of Native Mexicans whose maternal and paternal lineages reveal different narratives of their population history, with sex-biased continental contributions and different admixture proportions. At a continental scale, we found that Arctic populations and the northernmost groups from North America cluster together, but we did not find a clear differentiation within Mesoamerica and the rest of the continent, which coupled with the fact that the majority of individuals from Central and South American samples are restricted to the Q-M3 branch, supports the notion that most Native Americans from Mesoamerica southwards are descendants from a single wave of migration. This observation is compatible with the idea that present day Mexico might have constituted an area of transition in the diversification of paternal lineages during the colonization of the Americas.

Linguistic and maternal genetic diversity are not correlated in Native Mexicans.

Mesoamerica, defined as the broad linguistic and cultural area from middle southern Mexico to Costa Rica, might have played a pivotal role during the colonization of the American continent. The Mesoamerican isthmus has constituted an important geographic barrier that has severely restricted gene flow between North and South America in pre-historical times. Although the Native American component has been already described in admixed Mexican populations, few studies have been carried out in native Mexican populations. In this study, we present mitochondrial DNA (mtDNA) sequence data for the first hypervariable region (HVR-I) in 477 unrelated individuals belonging to 11 different native populations from Mexico. Almost all of the Native Mexican mtDNAs could be classified into the four pan-Amerindian haplogroups (A2, B2, C1, and D1); only two of them could be allocated to the rare Native American lineage D4h3. Their haplogroup phylogenies are clearly star-like, as expected from relatively young populations that have experienced diverse episodes of genetic drift (e.g., extensive isolation, genetic drift, and founder effects) and posterior population expansions. In agreement with this observation, Native Mexican populations show a high degree of heterogeneity in their patterns of haplogroup frequencies. Haplogroup X2a was absent in our samples, supporting previous observations where this clade was only detected in the American northernmost areas. The search for identical sequences in the American continent shows that, although Native Mexican populations seem to show a closer relationship to North American populations, they cannot be related to a single geographical region within the continent. Finally, we did not find significant population structure in the maternal lineages when considering the four main and distinct linguistic groups represented in our Mexican samples (Oto-Manguean, Uto-Aztecan, Tarascan, and Mayan), suggesting that genetic divergence predates linguistic diversification in Mexico.

[Hemoglobin S frequency in five Mexican populations and its importance in public health]. / Frecuencia de la hemoglobina S en cinco poblaciones mexicanas y su importancia en la salud pública.

OBJECTIVE: To provide information regarding the heterozygote frequency for hemoglobin S (HbS) in five Mexican populations, the Haplotype in five S chromosomes, and underscore its importance for public health. MATERIAL AND METHODS: A total of 162 samples from three Nahua populations (Atocpan and Tlacotenco, DF, and Ixhuatlancillo, Veracruz) and 131 from mestizo populations (Coyolillo and Poza Rica, Veracruz) were studied after obtaining informed consent. The hemoglobin type was determined by electrophoresis, and DNA in leucocytes was obtained from five HbS samples. The haplotype was determined by PCR and cut with restrictases, according to literature. RESULTS: We found one heterozygote for hemoglobin S (0.6%) among Nahua and 18 among Mestizo groups (13.7%). Four haplotypes were Bantu and one was Benin. CONCLUSIONS: These findings are important to public health for populations with a high frequency of HbS, to inform and provide genetic counseling for carriers and medical attention to patients.

Characterization of mtDNA haplogroups in 14 Mexican indigenous populations.

In this descriptive study we investigated the genetic structure of 513 Mexican indigenous subjects grouped in 14 populations (Mixteca-Alta, Mixteca-Baja, Otomi, Purépecha, Tzeltal, Tarahumara, Huichol, Nahua-Atocpan, Nahua-Xochimilco, Nahua-Zitlala, Nahua-Chilacachapa, Nahua-Ixhuatlancillo, Nahua-Necoxtla, and Nahua-Coyolillo) based on mtDNA haplogroups. These communities are geographically and culturally isolated; parents and grandparents were born in the community. Our data show that 98.6% of the mtDNA was distributed in haplogroups A1, A2, B1, B2, C1, C2, D1, and D2. Haplotype X6 was present in the Tarahumara (1/53) and Huichol (3/15), and haplotype L was present in the Nahua-Coyolillo (3/38). The first two principal components accounted for 95.9% of the total variation in the sample. The mtDNA haplogroup frequencies in the Purépecha and Zitlala were intermediate to cluster 1 (Otomi, Nahua-Ixhuatlancillo, Nahua-Xochimilco, Mixteca-Baja, and Tzeltal) and cluster 2 (Nahua-Necoxtla, Nahua-Atocpan, and Nahua-Chilacachapa). The Huichol, Tarahumara, Mixteca-Alta, and Nahua-Coyolillo were separated from the rest of the populations. According to these findings, the distribution of mtDNA haplogroups found in Mexican indigenous groups is similar to other Amerindian haplogroups, except for the African haplogroup found in one population.

FMR1 CGG repeat distribution and linked microsatellite-SNP haplotypes in normal Mexican Mestizo and indigenous populations.

The (CGG)n repeat size distribution in the FMR1 gene was studied in healthy individuals: 80 X chromosomes of Mexican Mestizos from Mexico City and 33 X chromosomes of Mexican Amerindians from three indigenous communities (Purepechas, Nahuas, and Tzeltales), along with alleles and haplotypes defined by two microsatellite polymorphic markers (DXS548 and FRAXAC1) and two single nucleotide polymorphisms (FMRA and FMRB). Genetic frequencies of Mestizo and Amerindian subpopulations were statistically similar in almost all cases and thus were considered one population for comparisons with other populations. Sixteen (CGG)n alleles in the 17-38 size range were observed, and the most common were the 25 (38.0%), 26 (28.3%), and 24 (12.3%) repeat alleles. This pattern differs from most other populations reported, but a closer relation to Amerindian, European, and African populations was found, as expected from the historical admixture that gave rise to Mexican Mestizos. The results of the CA repeats analysis at DXS548-FRAXAC1 were restricted to nine haplotypes, of which haplotypes 7-4 (52.2%), 8-4 (23.8%), and 7-3 (11.5%) were predominant. The modal haplotype 7-4, instead of the nearly universal haplotype 7-3, had been reported exclusively in Eastern Asian populations. Likewise, only seven different FRAXAC1-FMRA-FMRB haplotypes were observed, including five novel haplotypes (3TA, 4TA, 3 - A, 4 - A, and 5 - A), compared with Caucasians. Of these, haplotypes - A (78.7%) and 3 - A (13.2%) were the most common in the Mexican population. These data suggest a singular but relatively low genetic diversity at FMR1 in the studied Mexican populations that may be related to the recent origin of Mestizos and the low admixture rate of Amerindians.

Frecuencia de la hemoglobina S en cinco poblaciones mexicanas y su importancia en la salud pública / Hemoglobin S frequency in five Mexican populations and its importance in public health

OBJETIVO: Informar la frecuencia de heterocigotos para la hemoglobina S (HbS) en cinco poblaciones mexicanas y el haplotipo en cinco muestras con HbS y subrayar su relevancia en la salud pública. MATERIAL Y MÉTODOS: Se tomó una muestra de sangre periférica en 162 individuos no relacionados provenientes de tres poblaciones nahuas (Atocpan y Tlacotenco, DF, e Ixhuatlancillo, Veracruz), y en 131 mestizos (Coyolillo y Poza Rica, Veracruz), previo consentimiento informado. Se determinó el tipo de hemoglobina por electroforesis y se extrajo el DNA de leucocitos de cinco muestras en las que se determinó el haplotipo por PCR y corte con restrictasas. RESULTADOS: Entre los nahuas se reconoció un heterocigoto HbAS (0.6 por ciento) y 18 en mestizos (13.7 por ciento). Se identificaron cuatro haplotipos Bantu y uno Benin. CONCLUSIONES: Estos hallazgos son importantes en términos de la salud pública en poblaciones con alta frecuencia de HbS, para dar información y consejo genético a los portadores y la atención médica oportuna y adecuada a los pacientes.

OBJECTIVE: To provide information regarding the heterozygote frequency for hemoglobin S (HbS) in five Mexican populations, the Haplotype in five S chromosomes, and underscore its importance for public health. MATERIAL AND METHODS: A total of 162 samples from three Nahua populations (Atocpan and Tlacotenco, DF, and Ixhuatlancillo, Veracruz) and 131 from mestizo populations (Coyolillo and Poza Rica, Veracruz) were studied after obtaining informed consent. The hemoglobin type was determined by electrophoresis, and DNA in leucocytes was obtained from five HbS samples. The haplotype was determined by PCR and cut with restrictases, according to literature. RESULTS:We found one heterozygote for hemoglobin S (0.6 percent) among Nahua and 18 among Mestizo groups (13.7 percent). Four haplotypes were Bantu and one was Benin. CONCLUSIONS: These findings are important to public health for populations with a high frequency of HbS, to inform and provide genetic counseling for carriers and medical attention to patients.