Polynesian mtDNA in extinct Amerindians from Brazil

From the paper:

In 1808 the Portuguese Crown declared “Just War” (Bellumiustum) against all Indian tribes that did not accept European laws (23). The fierce Botocudo were targeted in such wars and, in consequence, became virtually extinct by the end of the 19th century (24). Their importance for the history of the peopling of the Americas was revealed by studies reporting that the Botocudo had cranial features that consistently were described as intermediate between the polar Paleoamerican and Mongoloid morphologies (25, 26). Multivariate analyses of the cranial measures of different Amerindian and Paleoamerican groups from Brazil indeed concluded that the Botocudo Indians presented sufficient similarities with the Lagoa Santa Paleoamericans to be considered candidates to be their possible descendants (27).

Possible explanations:

The first scenario, prehistoric, is related to the possibility of genetic continuity between the Paleoamericans from Lagoa Santa and Botocudo Indians (26, 27, 37), which indeed originally had motivated this study. 

... 

Another imaginable pre-Columbian scenario involves opportunities for more recent direct contact between Polynesia and South America before the European arrival. Such possibility of a direct movement from Oceania across the Pacific Ocean to the Americas was raised by Cann (43) on a discussion of the origin of the Amerindian B haplogroup. This finding prompted Bonatto et al. (44) to evaluate the likelihood of a Polynesian-Amerindian contact having occurred and conclude against it, although they could rule out neither minor contact events nor nonmaternal genetic exchange. New evidence from human and nonhuman material has become available since then. For example, there were archeological findings of Polynesian chicken bones in the Arauco Peninsula, in Chile (45) and evidence has been found in Easter Island of pre-Columbian presence of sweet potato and bottle gourd, both typical of South America (46, 47). Independent of the plausibility or implausibility of the pre-Columbian arrival of Polynesians to the South American Pacific coast, there still would remain the need to explain how these migrants crossed the Andes and ended up in Minas Gerais, Brazil. We feel that such a scenario is too unlikely to be seriously entertained. 

... 

The last scenario that we wish to assess is the possible arrival of Polynesian haplogroups to Brazil in modern times through the African slave trade from Madagascar, where 20% of the mtDNA lineages belong to the B4a1a1a haplogroup (29).

It may be of relevance that both Tianyuan (~40ka) and Boshan (~8ka) from China belong to mtDNA haplogroup B and that B belongs to the R (and N) clade of the mtDNA phylogeny, i.e., a different branch of Out-of-Africa than C (which belongs to M). I wager that interesting things were taking place in East Eurasia and the New World until fairly recent times, and hopefully ancient DNA will help us complete the picture.

PNAS doi: 10.1073/pnas.1217905110

Identification of Polynesian mtDNA haplogroups in remains of Botocudo Amerindians from Brazil

Vanessa Faria Gonçalves et al.

There is a consensus that modern humans arrived in the Americas 15,000–20,000 y ago during the Late Pleistocene, most probably from northeast Asia through Beringia. However, there is still debate about the time of entry and number of migratory waves, including apparent inconsistencies between genetic and morphological data on Paleoamericans. Here we report the identification of mitochondrial sequences belonging to haplogroups characteristic of Polynesians in DNA extracted from ancient skulls of the now extinct Botocudo Indians from Brazil. The identification of these two Polynesian haplogroups was confirmed in independent replications in Brazil and Denmark, ensuring reliability of the data. Parallel analysis of 12 other Botocudo individuals yielded only the well-known Amerindian mtDNA haplogroup C1. Potential scenarios to try to help understand these results are presented and discussed. The findings of this study may be relevant for the understanding of the pre-Columbian and/or post-Columbian peopling of the Americas.

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Abstracts from AAPA 2010

Some abstracts from the upcoming (April 14-17) meeting of the American Association of Physical Anthropologists.

Why are pygmies small? An anthropometrical and anthropogenetical question

NOEMIE BECKER et al.

Pygmy populations from central Africa have the shortest stature worldwide. The name “pygmy” indeed comes from the Greek “pugmaios” that is a measure of length. This reduced stature has been the subject of numerous endocrinological studies and many evolutionary hypotheses have suggested that this phenotype was an adaptation to the rainforest (hot, humid and dense environment), to alimentation or due to life history trade-offs (high mortality). We have anthropometrical data for a sample of more than 1000 individuals from 7 pygmy populations and 3 neighbouring farmer populations from Gabon, Cameroon and Central African Republic. DNA samples are also available for a large number of individuals. The analysis of anthropometrical data shows that all pygmy groups have a male mean stature under 160 cm (this was used in the definition settled by Cavalli-Sforza in1986) and that a high variability exists between various pygmy populations. Verdu et al. (2009) published a genetic analysis based on neutral microsatellites on the same populations and found that pygmies present a variable admixture proportion with nonpygmies. Comparing this data with our anthropometrical data at the individual level we find a strong correlation between level of admixture and stature, thus strongly supporting the existence of a genetic component in pygmy short stature. We developed a candidate-gene approach to search for such genetic factor and will present current results on various genes located in the GH-IGF1 axis.

New evidence on headshaping from the Early Byzantine Maroneia in Thrace, Greece.

PARASKEVI TRITSAROLI

The first case of headshaping from Early Byzantine Greece was identified in 2006 at the cemetery of Maroneia (5th-6th c. A.D.). Biocultural evidence suggested the presence of a female individual culturally linked to Hunic traditions. This paper analyzes the second case of headshaping on a female skeleton uncovered in 2009 and allows for the wider discussion of the presence of a larger group related to the Huns in the city of Maroneia. The skull was examined by combining macroscopic observation and x-ray. Points of pressure are recorded in the frontal, post-coronal and occipital regions resulting in an undulation of diploic bone. Possible bilateral pressure on the frontal bone has produced an artificially narrowed frontal. The skull extends posterosuperiorly. These features suggest the application of bandaging producing circular modification. Both headshaped skulls exhibit the same type of modification. Similarly, both women were buried in a supine position, without offerings, just like the remaining 36 deceased individuals in the cemetery of Maroneia. Headshaping was unknown among Byzantine customs. On the contrary, the Huns who attacked the Balkans twice and who unsuccessfully threatened Maroneia in 411 practiced a pronounced form of circular headshaping. Consequently, biocultural evidence strongly supports the hypothesis that a group linked to the Huns was installed at the city and was assimilated into this Early Byzantine society. Future biogeochemical analysis needs to be undertaken in order to investigate migration patterns. However, headshaping reflects the cosmopolitan character of Maroneia, an important urban center in a province of the Byzantine Empire.

The genetic legacy of indigenous Caribbean peoples: Evidence from autosomal and mitochondrial data.

JADA BENN TORRES et al.

Archeological evidence suggests that autochthonous peoples began to migrate into the eastern island chain in the Caribbean, known as the Lesser Antilles, as early as 7200 years BP. Upon the arrival of Europeans, an estimated 2-4 million people lived on these islands. Within 32 years of contact, the native populations had virtually disappeared from the region due to European-introduced disease, abuse, and genocide. This lead many scholars to conclude that indigenous Caribbean people had become extinct. However, small pockets of indigenous communities have survived and are present today on several Lesser Antillean islands. Furthermore, ethnohistoric data suggests that gene flow occurred between autochthonous peoples and enslaved Africans beginning in the colonial period. In this study, we examine the genetic legacy of autochthonous Caribbean peoples from the Lesser Antilles in contemporary African- Caribbean populations as evidenced from mitochondrial data and novel autosomal data. A total of 516 individuals from eight Caribbean islands were typed for 109 ancestry informative markers and a subset of individuals were also typed for their mitochondrial haplogroup. Mitochondrial haplogroups indicate that 5% of the sample has indigenous ancestry while admixture estimates from autosomal markers show 4% indigenous ancestry. Both lines of data suggest that despite the dramatic postcontact decline in population size, indigenous Caribbean people have made notable genetic contributions to contemporary African-Caribbean populations. Furthermore, these genetic contributions vary according to the genetic system typed and across the islands.

Chuvash origins: Evidence frommtDNA Markers.

ORION M. GRAF et al.

A sample of 96 unrelated individuals from Chuvashia, Russia was sequenced for hypervariable region-I (HVR-I) of the mtDNA molecule. The Chuvash speak a Turkic language that is not mutually intelligible to other extant Turkish groups, and their genetics are distinct from Turkic-speaking Altaic groups. Some scholars have suggested that they are remnants of the Golden Horde, while others have advocated that they are the products of admixture between Turkic and Finno-Ugric speakers who came into contact during the 13th century. Earlier genetic research using autosomal DNA markers suggested a Finno-Ugric origin for the Chuvash. This study examines non-recombining DNA markers to better elucidate their origins. The majority of individuals in this sample exhibit haplogroups H (31%), U (22%), and K (11%), all representative of western and northern Europeans, but absent in Altaic or Mongolian populations. Multidimensional scaling (MDS) was used to examine distances between the Chuvash and 8 reference populations compiled from the literature. Mismatch analysis showed a unimodal distribution. Along with neutrality tests (Tajima’s D (-1.43365) p less than 0.05, Fu’s FS (-25.50518) p less than 0.001), the mismatch distribution is suggestive of an expanding population. These tests suggest that the Chuvash are not related to the Altai and Mongolia along their maternal line but supports the “Elite” hypothesis that their language was imposed by a conquering group-- leaving Chuvash mtDNA largely of Eurasian origin with a small amount of Central Asian gene flow. Their maternal markers appear to most closely resemble Finno-Ugric speakers rather than fellow Turkic speakers.

Population history and substructure of Anatolia and Turkey as evidenced by craniofacial diversity.

NORIKO SEGUCHI et al.

Anatolia, the Asian segment of Turkey, is an area of evolutionary importance for human groups who used this corridor as a bridge for migration between the Caucasus, Western Asia and Europe since Lower Paleolithic times. Historically, Anatolia has been occupied by diverse civilizations, including the Byzantine and Ottoman Empires. This study is an attempt to understand Turkish population substructure and history by examining craniofacial diversity through several temporal periods framed within a population genetic model. If the region of Anatolia has been used as a migratory corridor for peoples spanning disparate geographic areas (Balkans, Central Asia, and East Asia), then gradual craniofacial change is expected due to these migrations coupled with extensive admixture. Studies using mtDNA indicate a pre-Neolithic expansion resulting in extensive migration, while Y chromosome studies reveal haplogroup clustering and gene flow from the Caucus with less admixture from Central and East Asia. Overall, our results indicate minimal Turkish population substructure. When crania were separated into sex, our results are consistent with uniparental marker population history. Female crania show a distinctness with modern groups and are actually more similar to Neolithic European and Near Eastern populations. This would indicate a relatively stable female population in Anatolia since Neolithic times. Male crania are more heterogeneous and cluster within a larger geographic zone of Eurasia and the Near East consistent with greater male migration. There is little support for admixture from Central or East Asian groups. These results support the hypothesis for a Turkic language displacement with insignificant genetic exchange.

Genetic analyses reveal a history of serial founder effects, admixture between longseparated founding populations in Oceania, and interbreeding with archaic humans.

SARAH JOYCE, KEITH HUNLEY

Genetic anthropologists continue to debate whether human neutral genetic variation primarily reflects a continuum of demes connected by local gene flow or colonization and serial founder effects. A second unresolved issue concerns the genetic contribution of archaic species to the modern human gene pool. Some studies suggest that this contribution was substantial and that it played an important role in human adaptation. These issues remain unresolved because of inadequacies and biases in datasets, problems in statistical methodology, and the failure to recognize that different evolutionary processes may produce similar outcomes. This study redresses these limitations by analyzing gene identity within and between populations in a dataset comprised of 614 STRs assayed in 1,983 people from 99 widespread populations. Our strategy is to fit hierarchical models to these data and examine residual deviations from the models. Each model involves nesting smaller units such as populations into larger units such as continental regions. It is possible to restate many of these models as either expansions or reductions of each other and thereby identify aspects of population structure that have had a major impact on the overall pattern of diversity. The strong fit of a model estimated using the Neighbor Joining algorithm indicates that human genetic diversity primarily reflects a history of successive founder effects associated with our exodus from Africa, not a continuum of demes connected by gene flow. Residual deviations from the model suggest: 1) the genomes of Oceanic peoples are the product of two independent waves of migration to the region and admixture, and 2) genetic exchange occurred between archaic and modern humans after their initial divergence.

Correlations between genetic ancestry and superficial traits indicate substantial admixture stratification in Brazil.

LAUREL N. PEARSON et al.

Brazil is one of the most admixed countries in the world. How this admixture affected the distribution of genetic ancestry across Brazilian ethnic (“Color”) groups is a fundamental question which to date has only received minimal attention. In an effort to systematically study variation in genetic ancestry in Brazil, we collected DNA and various phenotypic measures from 596 volunteers in Brasilia, Brazil. Participants were asked to provide their self-described “Color” as defined by the Brazilian census (Preta/Black, Parda/Brown, Branca/White, Indigena/Indigenous, Amarela/Yellow). Phenotype data was collected from each subject including hair texture, highresolution eye photographs, skin and hair color by reflectometry, and three-dimensional facial photographs. To estimate genomic ancestry, DNA from each participant was genotyped using 176 ancestry informative markers (AIMs), autosomal SNPs with large frequency differences between parental populations known to contribute to Brazilian admixture (West African, East Asian, European and Indigenous American). Although genomic ancestry shows significant overlap across “Color” groups, there are highly significant differences in average proportional ancestry. Additionally, analyses comparing trait values and genetic ancestry show significant correlations consistent with expectations of populations stratified with respect to genetic ancestry. Ethnographic research indicates that designations of “Color” are fluid and largely based on physical traits as opposed to known ancestry. This likely contributes to the observed ancestry overlap between ethnic groups and the strong association between phenotype and group. This study emphasizes the importance of genetic marker based estimates of ancestry as well as objective assessment of superficial traits in understanding the admixture process.

Geographic structure of genetic variation in North America: Population fissions and European admixture.

KARI BRITT SCHROEDER et al.

A satisfactory understanding of how modern Native North America populations are biologically related to each other requires increased sampling of populations and/or genetic markers and testing of the fit of different models of population structure. To this end, we combine new autosomal microsatellite data from Native North American populations with previously published data. Using J.C. Long’s Generalized Hierarchical Modeling software, we evaluate the fit of different trees to the data. Although we observe a correlation between population pairwise genetic and geographic distances, as expected with a long-term process of isolation by distance, we show that this correlation likely results from geographically-structured population fissions. This pattern could result from the initial peopling of North America or from a later process. The magnitude of European ancestry in the sampled populations, as estimated with the software structure, varies drastically among geographic regions, and may limit our ability to use modern genetic variation to investigate Native North American prehistory.This study was funded by the Wenner-Gren Foundation for Anthropological Research, grant number 7580 to K.B. Schroeder and D.G. Smith, and by the National Science Foundation, grant BCS- 0422144 to R.S. Malhi, B.M. Kemp, and D.G. Smith.

Coalescent modeling of Yakut origins points to small founding population based on mtDNA variation.

MARK ZLOJUTRO et al.

Based on archaeological and ethnohistorical evidence, the Yakut people of northeastern Siberia are considered to be descendants of ancient Turkic-speaking populations once living in the distant Altai- Sayan region on the Russian- Mongolian border. The results of phylogeographic studies on Siberian mtDNA variation have been generally concordant with a southern Yakut origin, although the timing of the northern migration, the size of the founder group and the degree of genetic admixture with non-Turkic Siberian populations are less apparent. In an effort to better understand Yakut origins, we modeled 25 demographic scenarios, including parameters such as effective population size, growth rate and gene flow, and tested by coalescent simulation whether any are consistent with the patterns of mtDNA diversity observed in present-day Yakuts. The models consist of either two simulated demes that represent Yakuts and a South Siberian ancestral population, or three demes that also include a regional Northeast Siberian population that served as a source of localized gene flow into the Yakut deme. The model that produced the best fit to the observed data defined a founder group with an effective female population size of only 150 individuals, migrating northwards approximately 1,000 years BP and undergoing significant admixture with neighboring populations in Northeastern Siberia. These simulation results indicate a pronounced founder effect that was primarily kin-structured and reconcile reported discrepancies between Yakut mtDNA and Y chromosome diversity levels.

The role of selection-nominated candidate genes in determining Indigenous American skin pigmentation.

ELLEN E QUILLEN et al.

World-wide variability in skin pigmentation has been a subject of anthropological inquiry from the beginning of our discipline. Recent genomic studies indicate that skin pigmentation is one of the most rapidly evolving phenotypes in many human populations and that genes underlying skin pigmentation have been subject to some of the most extreme selective pressures of any genes in the human genome. Unlike previous research, this study both identifies pigmentation genes that have undergone selection in Indigenous American populations and tests the influences of these genes on skin color in admixed individuals. 906,600 single nucleotide polymorphisms (SNPs) were surveyed for signatures of selection in indigenous populations from Central and South America. Evidence of selection was identified by comparison to HapMap Phase I populations using reduction in heterozygosity (lnRH), Locus- Specific Branch Length (LSBL), Tajima’s D, and haplotype block structure. In the 12 pigmentation candidate genes that show the strongest evidence of selection (ADAM17, POMC, AP3B1, OPRM1, SILV, OCA2/HERC, PLDN, MYO5A, RAB27A, CYP1A2, ATRN, and ASIP), 48 SNPs selected to represent the overall variation in the selection nominated candidate genes were genotyped in individuals of admixed Indigenous American and European ancestry. These SNPs show substantial allele frequency differences between the parental populations. Using admixture based regression model analyses, genes contributing to darker skin pigmentation in Indigenous Americans were found. This study not only identified skin pigmentation genes contributing to skin color variation in previously understudied Indigenous American populations, it validated the usefulness of using population genetic tests of selection to identify functional genes. This study was generously funded by the National Science Foundation Dissertation Improvement Grant 0925976

Variable genetic ancestry in Brazilians

Braz J Med Biol Res. 2009 Sep 11. pii: S0100-879X2009005000026.

DNA tests probe the genomic ancestry of Brazilians.

Pena SD, Bastos-Rodrigues L, Pimenta JR, Bydlowski SP.

We review studies from our laboratories using different molecular tools to characterize the ancestry of Brazilians in reference to their Amerindian, European and African roots. Initially we used uniparental DNA markers to investigate the contribution of distinct Y chromosome and mitochondrial DNA lineages to present-day populations. High levels of genetic admixture and strong directional mating between European males and Amerindian and African females were unraveled. We next analyzed different types of biparental autosomal polymorphisms. Especially useful was a set of 40 insertion-deletion polymorphisms (indels) that when studied worldwide proved exquisitely sensitive in discriminating between Amerindians, Europeans and Sub-Saharan Africans. When applied to the study of Brazilians these markers confirmed extensive genomic admixture, but also demonstrated a strong imprint of the massive European immigration wave in the 19th and 20th centuries. The high individual ancestral variability observed suggests that each Brazilian has a singular proportion of Amerindian, European and African ancestries in his mosaic genome. In Brazil, one cannot predict the color of persons from their genomic ancestry nor the opposite. Brazilians should be assessed on a personal basis, as 190 million human beings, and not as members of color groups.

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Genetic composition of Brazilian population (Lins et al. 2009)

American Journal of Human Biology doi:10.1002/ajhb.20976

Genetic composition of Brazilian population samples based on a set of twenty-eight ancestry informative SNPs

Tulio C. Lins et al.

Abstract

Ancestry informative SNPs can be useful to estimate individual and population biogeographical ancestry. Brazilian population is characterized by a genetic background of three parental populations (European, African, and Brazilian Native Amerindians) with a wide degree and diverse patterns of admixture. In this work we analyzed the information content of 28 ancestry-informative SNPs into multiplexed panels using three parental population sources (African, Amerindian, and European) to infer the genetic admixture in an urban sample of the five Brazilian geopolitical regions. The SNPs assigned apart the parental populations from each other and thus can be applied for ancestry estimation in a three hybrid admixed population. Data was used to infer genetic ancestry in Brazilians with an admixture model. Pairwise estimates of Fst among the five Brazilian geopolitical regions suggested little genetic differentiation only between the South and the remaining regions. Estimates of ancestry results are consistent with the heterogeneous genetic profile of Brazilian population, with a major contribution of European ancestry (0.771) followed by African (0.143) and Amerindian contributions (0.085). The described multiplexed SNP panels can be useful tool for bioanthropological studies but it can be mainly valuable to control for spurious results in genetic association studies in admixed populations.

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MHC-dissimilar mating in Brazil

This seems to parallel previous findings on European Americans.

Opposites attract -- how genetics influences humans to choose their mates

Vienna, Austria: New light has been thrown on how humans choose their partners, a scientist will tell the annual conference of the European Society of Human Genetics today (Monday May 25). Professor Maria da Graça Bicalho, head of the Immunogenetics and Histocompatibility Laboratory at the University of Parana, Brazil, says that her research had shown that people with diverse major histocompatibility complexes (MHCs) were more likely to choose each other as mates than those whose MHCs were similar, and that this was likely to be an evolutionary strategy to ensure healthy reproduction.

Females' preference for MHC dissimilar mates has been shown in many vertebrate species, including humans, and it is also known that MHC influences mating selection by preferences for particular body odours. The Brazilian team has been working in this field since 1998, and decided to investigate mate selection in the Brazilian population, while trying to uncover the biological significance of MHC diversity.

The scientists studied MHC data from 90 married couples, and compared them with 152 randomly-generated control couples. They counted the number of MHC dissimilarities among those who were real couples, and compared them with those in the randomly-generated 'virtual couples'. "If MHC genes did not influence mate selection", says Professor Bicalho, "we would have expected to see similar results from both sets of couples. But we found that the real partners had significantly more MHC dissimilarities than we could have expected to find simply by chance."

Within MHC-dissimilar couples the partners will be genetically different, and such a pattern of mate choice decreases the danger of endogamy (mating among relatives) and increases the genetic variability of offspring. Genetic variability is known to be an advantage for offspring, and the MHC effect could be an evolutionary strategy underlying incest avoidance in humans and also improving the efficiency of the immune system, the scientists say.

The MHC is a large genetic region situated on chromosome 6, and found in most vertebrates. It plays an important role in the immune system and also in reproductive success. Apart from being a large region, it is also an extraordinarily diverse one.

"Although it may be tempting to think that humans choose their partners because of their similarities", says Professor Bicalho, "our research has shown clearly that it is differences that make for successful reproduction, and that the subconscious drive to have healthy children is important when choosing a mate."

The scientists believe that their findings will help understanding of conception, fertility, and gestational failures. Research has already shown that couples with similar MHC genes had longer intervals between births, which could imply early, unperceived miscarriages. "We intend to follow up this work by looking at social and cultural influences as well as biological ones in mate choice, and relating these to the genetic diversity of the extended MHC region", says Professor Bicalho.

"We expect to find that cultural aspects play an important role in mate choice, and certainly do not subscribe to the theory that if a person bears a particular genetic variant it will determine his or her behaviour. But we also think that the unconscious evolutionary aspect of partner choice should not be overlooked. We believe our research shows that this has an important role to play in ensuring healthy reproduction, by helping to ensure that children are born with a strong immune system better able to cope with infection."

I had previously posted some more abstracts from ESHG 2009. Here is the abstract from this study:

New evidences about MHC-based patterns of mate choice

M. Bicalho, J. da Silva, J. M. Magalhães, W. Silva;

Major Histocompatibility Complex (MHC) genes code for cell surface proteins, which plays an important role in immune recognition. In the late 1970s, Yamazaki observed that inbred mice were more likely to mate with partners having MHC dissimilar genes. Females’ preference for MHC dissimilar mates was also observed in other vertebrate species, including humans. It has been shown that MHC influences mating selection mediated by preferences based on body odor. What’s the functional significance of these findings, if some? It was assumed that through olfactory cues MHC-related evolved as a strategy to maximize the offspring MHC heterozygosity. Parents with dissimilar MHCs could provide their offspring with a better chance to ward infections off because their immune system genes are more diverse. MHC genotype might be used to signal relatedness and immune response genotypes through.

We investigated whether husband-wife couples (n=90) obtained from LIGH’s database were more MHC-similar/dissimilar in comparison to random couples generated from the same database (n=55 000) as to collect evidence of MHC influence in MHC-based patterns of mate choice.

The individuals HLA typing (Class I and Class II) was performed by PCR-SSP or PCR-rSSOP using a commercial kit ( One Lambda Inc., Canoga Park. CA, USA).

Our results and comparisons ( p= 0,014) suggest that couples seem to be formed by individuals with less HLA similarity, corroborating the hypothesis that HLA antigens, especially Class I, may influence mate selection and marriages in humans.

Phylogeography of African Brazilians

Hum Hered. 2008 Jul 25;65(1):23-32 [Epub ahead of print]

The Phylogeography of African Brazilians.

Gonçalves VF, Carvalho CM, Bortolini MC, Bydlowski SP, Pena SD.

Background/Aims: Approximately four million Africans were taken as slaves to Brazil, where they interbred extensively with Amerindians and Europeans. We have previously shown that while most White Brazilians carry Y chromosomes of European origin, they display high proportions of African and Amerindian mtDNA lineages, because of sex-biased genetic admixture. Methods: We studied the Y chromosome and mtDNA haplogroup structure of 120 Black males from Sao Paulo, Brazil. Results: Only 48% of the Y chromosomes, but 85% of the mtDNA haplogroups were characteristic of sub-Saharan Africa, confirming our previous observation of sexually biased mating. We mined literature data for mtDNA and Y chromosome haplogroup frequencies for African native populations from regions involved in Atlantic Slave Trade. Principal Components Analysis and Bayesian analysis of population structure revealed no genetic differentiation of Y chromosome marker frequencies between the African regions. However, mtDNA examination unraveled considerable genetic structure, with three clusters at Central-West Africa, West Africa and Southeast Africa. A hypothesis is proposed to explain this structure. Conclusion: Using these mtDNA data we could obtain for the first time an estimate of the relative ancestral contribution of Central-West (0.445), West (0.431) and Southeast Africa (0.123) to African Brazilians from Sao Paulo. These estimates are consistent with historical information. Copyright (c) 2008 S. Karger AG, Basel.

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