Uniparental ancestry markers in Chilean populations

An approach on the migratory processes in the north of Chile based on Y chromosome analysis

OBJECTIVES

Northern Chile is an area characterized by a complex cultural and demographic trajectory. During the last few centuries, this complex trajectory has become the destination of intra- and intercontinental migratory waves. In this study, we analyzed the Y chromosome to evaluate how migratory and admixture patterns have affected the genetic composition of the populations in northern Chile compared with other populations of the country.

METHODS

A total of 311 people from urban (Antofagasta and Calama), rural (Azapa and Camarones), and Native (Aymara and Atacameño) populations from northern Chile were characterized by 26 SNPs and the STR DYS393 of the Y chromosome, along with 69 individuals from Native populations (Mapuche, Pehuenche, and Huilliche) from southern Chile. In addition to characterizing the paternal lineages, multivariate analyses were performed to compare with published data from other Chilean populations.

RESULTS

Both the Antofagasta and Calama populations show differences compared with the rest of the Chilean population. On one side, Antofagasta shows a high diversity of non-Amerindian lineages, including the highest value for haplogroup I (12%) for all Chileans populations. Otherwise, Calama has the highest value of any Chilean urban population (31.9%) for Amerindian lineages, including the only Q-M3 sub-lineage detected in the entire sample. Regarding the Native population, Aymara presents the highest percentage of Q-M3 (94.4%).

CONCLUSIONS

The Y chromosome haplogroup distribution allowed us to identify recent migratory processes typical of the northern populations studied. These have shaped the demographic and cultural dynamics of local and migrant groups in the territory.

Uniparental origins of the admixed Argentine Patagonia

OBJECTIVES

We aimed to contribute to the understanding of the ancient geographic origins of the uniparentally inherited markers in modern admixed Argentinian populations from central Patagonia with new information provided for the city of Trelew. We attempted to highlight the importance of combining different genetic markers when studying population history.

METHODS

The mtDNA control region sequence was typified in 89 individuals and 12 Y-STR and 15 Y-SNP loci were analyzed in 66 males. With these data, analysis of molecular variance and Network analyses were carried out. We exhaustively compared the modern data with ancient mtDNA information. Finally, we tested the differences in continental origins estimated by uniparental and previously published biparental markers.

RESULTS

Native American mtDNAs (53.9%) increased when maternal ancestors were born in the northern (81.8%) and southern (58.5%) regions of Argentina or in Chile (77.8%). Population substructure was only observed for Y-chromosome haplotypes. Some mtDNA haplogroups have been present in the area for at least ca. 2762-2430 and ca. 500 (D1g and D1g4 haplogroups) and ca. 6736 and ca. 6620 (C1b and C1c haplogroups) years, respectively. In contrast, haplogroups B2i2 and C1b13, frequent in modern Patagonia populations, had not been found in previous ancient DNA studies of the region.

CONCLUSIONS

The results suggest that Native American ancestry is well preserved in the region. Trelew samples had characteristic native mtDNA haplogroups previously described in Chilean and Argentine Patagonian populations, but not observed in ancient samples until now. These findings support the idea that these lineages have a recent regional origin. Finally, the estimated proportions of continental ancestry depend on the genetic marker analyzed.

The Chilean socio-ethno-genomic cline

Studies of the current Chilean population performed using classical genetic markers have established that the Chilean population originated primarily from the admixture of European people, particularly Spaniards, and Amerindians. A socioeconomic-ethno-genetic cline was established soon after the conquest. Spaniards born in Spain or Chile occupied the highest Socioeconomic Strata, while Amerindians belonged to the lowest. The intermediate strata consisted of people with different degrees of ethnic admixture; the larger the European admixture, the higher the Socioeconomic Level. The present study of molecular genomic markers sought to calculate the percentage of Amerindian admixture and revealed a finer distribution of this cline, as well as differences between two Amerindian groups: Aymara and Mapuche. The use of two socioeconomic classifications - Class and Socioeconomic Level - reveals important differences. Furthermore, Self-reported Ethnicity (self-assignment to an ethnic group) and Self-reported Ancestry (self-recognition of Amerindian ancestors) show variations and differing relationships between socioeconomic classifications and genomic Amerindian Admixture. These data constitute a valuable input for the formulation of public healthcare policy and show that the notions of Ethnicity, Socioeconomic Strata and Class should always be a consideration in policy development.

Ancestry and admixture of a southernmost Chilean population: The reflection of a migratory history

OBJECTIVES

Punta Arenas is a Chilean city situated on ancestral Aönikenk territory. The city was founded by 19th- and 20th-century colonists from Chile (Chiloé) and Europe (Croatia). This work uses uniparental and ancestry-informative markers (AIMs) to explore the effects of historic migratory and admixture patterns on the current genetic composition of Punta Arenas.

METHODS

We analyzed mitochondrial DNA (mtDNA), Y-chromosome single-nucleotide polymorphisms (SNPs), and 141 AIMs obtained from 129 DNA samples from male residents with regional ancestry. After characterizing uniparental lineages and ancestry proportions, multivariate analysis was used to explore relationships among the various types of data.

RESULTS

Punta Arenas has an admixed population with three main genetic components: European (56.5%), northern Native (11.3%), and south-central Native (28.6%). The Native component is preponderant in the mtDNA (83.76%), while the foreign component predominates in the Y-chromosome (92.25%). Non-Native mtDNA lineages are associated with European genetic ancestry, and Native mtDNA lineages originated mainly in the southern and southernmost regions of Chile. Most non-Native Y-chromosome SNPs originated in Spain, and secondly, in Croatia.

CONCLUSIONS

The population of Punta Arenas is mainly of Chilote origin with south-central Native and Spanish ancestral components, as well as some Croatian components. The persistence of local Native lineages is notable, suggesting continuity with the ancestral populations of the region such as the Kawésqar, Aönikenk, Yámana, or Selknam peoples. This study contributes to our knowledge of local history and its links to national and global developments in genetic ancestry.

The Genetic Population Structure of Robinson Crusoe Island, Chile

Studies examining genetic conditions common in Latin America are highly underrepresented in the scientific literature. Understanding of the population structure is limited, particularly Chile, in part due to the lack of available population specific data. An important first-step in elucidating disease mechanisms in Latin America countries is to understand the genetic structure of isolated populations. Robinson Crusoe Island (RCI) is a small land mass off the coast of Chile. The current population of over 900 inhabitants are primarily descended from a small number of founders who colonized the island in the late 1800s. Extensive genealogical records can trace the ancestry of almost the entire population. We perform a comprehensive genetic analysis to investigate the ancestry of the island population, examining ancestral mitochondrial and Y chromosome haplogroups, as well as autosomal admixture. Mitochondrial and Y chromosome haplogroups indicated a substantial European genetic contribution to the current RCI population. Analysis of the mitochondrial haplogroups found in the present-day population revealed that 79.1% of islanders carried European haplogroups, compared to 60.0% of the mainland Chilean controls from Santiago. Both groups showed a substantially lower contribution of indigenous haplogroups than expected. Analysis of the Y chromosome haplogroups also showed predominantly European haplogroups detected in 92.3% of male islanders and 86.7% of mainland Chilean controls. Using the near-complete genealogical data collected from the RCI population, we successfully inferred the ancestral haplogroups of 16/23 founder individuals, revealing genetic ancestry from Northern and Southern Europe. As mitochondrial and Y investigations only provide information for direct maternal and paternal lineages, we expanded this to investigate genetic admixture using the autosomes. Admixture analysis identified substantial indigenous genetic admixture in the RCI population (46.9%), higher than that found in the Santiago mainland Chilean controls (43.4%), but lower than a more representative Chilean population (Chile_GRU) (49.1%). Our study revealed the Robinson Crusoe Island population show a substantial genetic contribution for indigenous Chileans, similar to the level reported in mainland Chileans. However, direct maternal and paternal haplogroup analysis revealed strong European genetic contributions consistent with the history of the Island.

Development of a small panel of SNPs to infer ancestry in Chileans that distinguishes Aymara and Mapuche components

Background

Current South American populations trace their origins mainly to three continental ancestries, i.e. European, Amerindian and African. Individual variation in relative proportions of each of these ancestries may be confounded with socio-economic factors due to population stratification. Therefore, ancestry is a potential confounder variable that should be considered in epidemiologic studies and in public health plans. However, there are few studies that have assessed the ancestry of the current admixed Chilean population. This is partly due to the high cost of genome-scale technologies commonly used to estimate ancestry. In this study we have designed a small panel of SNPs to accurately assess ancestry in the largest sampling to date of the Chilean mestizo population (n = 3349) from eight cities. Our panel is also able to distinguish between the two main Amerindian components of Chileans: Aymara from the north and Mapuche from the south.

Results

A panel of 150 ancestry-informative markers (AIMs) of SNP type was selected to maximize ancestry informativeness and genome coverage. Of these, 147 were successfully genotyped by KASPar assays in 2843 samples, with an average missing rate of 0.012, and a 0.95 concordance with microarray data. The ancestries estimated with the panel of AIMs had relative high correlations (0.88 for European, 0.91 for Amerindian, 0.70 for Aymara, and 0.68 for Mapuche components) with those obtained with AXIOM LAT1 array. The country’s average ancestry was 0.53 ± 0.14 European, 0.04 ± 0.04 African, and 0.42 ± 0.14 Amerindian, disaggregated into 0.18 ± 0.15 Aymara and 0.25 ± 0.13 Mapuche. However, Mapuche ancestry was highest in the south (40.03%) and Aymara in the north (35.61%) as expected from the historical location of these ethnic groups. We make our results available through an online app and demonstrate how it can be used to adjust for ancestry when testing association between incidence of a disease and nongenetic risk factors.

Conclusions

We have conducted the most extensive sampling, across many different cities, of current Chilean population. Ancestry varied significantly by latitude and human development. The panel of AIMs is available to the community for estimating ancestry at low cost in Chileans and other populations with similar ancestry.

Genetic admixture patterns in Argentinian Patagonia

As in other Latin American populations, Argentinians are the result of the admixture amongst different continental groups, mainly from America and Europe, and to a lesser extent from Sub-Saharan Africa. However, it is known that the admixture processes did not occur homogeneously throughout the country. Therefore, considering the importance for anthropological, medical and forensic researches, this study aimed to investigate the population genetic structure of the Argentinian Patagonia, through the analysis of 46 ancestry informative markers, in 433 individuals from five different localities. Overall, in the Patagonian sample, the average individual ancestry was estimated as 35.8% Native American (95% CI: 32.2–39.4%), 62.1% European (58.5–65.7%) and 2.1% African (1.7–2.4%). Comparing the five localities studied, statistically significant differences were observed for the Native American and European contributions, but not for the African ancestry. The admixture results combined with the genealogical information revealed intra-regional variations that are consistent with the different geographic origin of the participants and their ancestors. As expected, a high European ancestry was observed for donors with four grandparents born in Europe (96.8%) or in the Central region of Argentina (85%). In contrast, the Native American ancestry increased when the four grandparents were born in the North (71%) or in the South (61.9%) regions of the country, or even in Chile (60.5%). In summary, our results showed that differences on continental ancestry contribution have different origins in each region in Patagonia, and even in each locality, highlighting the importance of knowing the origin of the participants and their ancestors for the correct interpretation and contextualization of the genetic information.

mtDNA structure: the women who formed the Brazilian Northeast

BACKGROUND

The distribution of mitochondrial DNA (mtDNA) lineages in Brazil is heterogeneous due to different regional colonization dynamics. Northeastern Brazil, although being an important region in terms of human imigration and ethnic admixture, has little information regarding its population mtDNA composition. Here, we determine which mitochondrial lineages contributed to the formation of the Northeastern Brazilian population. Our sample consisted of 767 individuals distributed as follows i) 550 individuals from eight Northeastern states (Piauí, Ceará, Rio Grande do Norte, Paraíba, Pernambuco, Alagoas, Sergipe, and Bahia) which were sequenced for mtDNA hypervariable segments I, II, and III; ii) 217 individuals from Alagoas and Pernambuco (previously published data). Data analysis was performed through sequence alignment and Haplogrep 2.0 haplogroup assignment tools. Furthermore, maternal ancestry distribution was contextualized and, when possible, related to historical events to better understand the biological interactions and population dynamics that occurred in this region since the beginning of colonization.

RESULTS

Unexpectedly, Amerindian mitochondrial ancestry was the highest in the Northeastern region overall, followed by African, European and non-Amerindian Asian, unlike previous results for this region. Alagoas and Pernambuco states, however, showed a larger African mtDNA frequency. The Northeastern region showed an intraregional heterogeneous distribution regarding ancestral groups, in which states/mesoregions located to the north had a prevalent Amerindian ancestral frequency and those to the south had predominance of African ancestry. Moreover, results showed great diversity of European haplogroups and the presence of non-Amerindian Asian haplogroups.

CONCLUSIONS

Our findings are in disagreement with previous investigations that suggest African mitochondrial ancestry is the most prevalent in the Brazilian Northeast. The predominance of Amerindian lineages exemplifies the importance of indigenous women in the formation of the population, despite intense African slave entry and conflicts with European settlers. The variable distribution of ancestral groups observed in the Northeast is in accordance with historical records showing the similarities with colonization dynamics occurred in the Amazon region and the Brazilian Southeast. Moreover, the variety of European haplogroups suggests multiple origins of founding groups, specially those found in Western European populations.