Ancestry Informative Markers Clarify the Regional Admixture Variation in the Costa Rican Population

Posted in Articles, Caribbean/Latin America, Health/Medicine/Genetics, Media Archive on 2014-04-05 19:48Z by Steven

Ancestry Informative Markers Clarify the Regional Admixture Variation in the Costa Rican Population

Human Biology
Volume 85, Number 5, October 2013
pages 721-740
DOI: 10.1353/hub.2013.0041

Rebeca Campos-Sánchez
Universidad de Costa Rica, San José, Costa Rica

Henriette Raventós, Associate Professor and Researcher
Universidad de Costa Rica, San José, Costa Rica

Ramiro Barrantes, Professor of Biology
Universidad de Costa Rica, San José, Costa Rica

The genetic structure of Costa Rica’s population is complex, both by region and by individual, due to the admixture process that started during the 15th century and historical events thereafter. Previous studies have been done mostly on Amerindian populations and the Central Valley inhabitants using various microsatellites and mitochondrial DNA markers. Here, we study for the first time a random sample from all regions of the country with ancestry informative markers (AIMs) to address the individual and regional admixture proportions. A sample of 160 male individuals was screened for 78 AIMs customized in a GoldenGate platform from Illumina. We observed that this small set of AIMs has the same power of hundreds of microsatellites and thousands of single-nucleotide polymorphisms to evaluate admixture, with the benefit of reducing genotyping costs. This type of investigation is necessary to explore new genetic markers useful for forensic and genetic investigation. Our data showed a mean admixture proportion of 49.2% European (EUR), 37.8% Native American (NAM), and 12.9% African (AFR), with a disproportionate admixture composition by region. In addition, when Chinese (CHB) was included as a fourth component, the proportions changed to 45.6% EUR, 33.5% NAM, 11.7% AFR, and 9.2% CHB. The admixture trend is consistent among all regions (EUR > NAM > AFR), and individual admixture estimates vary broadly in each region. Though we did not find stratification in Costa Rica’s population, gene admixture should be evaluated in future genetic studies of Costa Rica, especially for the Caribbean region, as it contains the largest proportion of African ancestry (30.9%).

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Analysis of a Tri-Racial Isolate

Posted in Anthropology, Articles, Media Archive, Native Americans/First Nation, Tri-Racial Isolates, United States on 2013-11-01 20:59Z by Steven

Analysis of a Tri-Racial Isolate

Human Biology
Volume 36, Number 4 (December 1964)
pages 362-373

William S. Pollitzer
Department of Anatomy
University of North Carolina, Chapel Hill

Based on a paper presented at the meeting of the American Association of Physical Anthropologists in Philadelphia, May 2, 1962

A relatively isolated population in the state of North Carolina, composed of persons who call themselves Indian but who appear to be of tri-racial origin, provides a model for the study of analysis by gene frequencies of a mixed population of White, Negro, and Indian ancestry.

A people considered Indian is known to have occupied this territory by the mid-eighteenth century; they spoke English, tilled the soil, and owned slaves. English, Scotch Highlanders, and French Huguenots migrated into the area in the eighteenth century also. Planters from neighboring states settled in this vicinity, often bringing slaves and a few free Negroes with them. The most common names of the free Negroes are the same as those of the present-day mixed population.

The origin of the Indian component of this hybrid population is open to speculation; three ideas have been advanced. The most colorful theory is that the people of the present isolate are the descendants of Raleigh’s famous “Lost Colony” who mixed with the Croatan Indians, an Algonquin-speaking tribe on the coast. Some similarity in the names of the colonists and the names in the present population, plus a few cultural traits, have been construed as evidence for this view. Another suggestion is that the Cherokee, a powerful Iroquois-speaking tribe who had general overlordship in the Western Carolinas, contributed the Indian genes to the hybrid group. Finally, the view has been advanced that the Siouan-speaking tribes who lived in the Piedmont Carolinas, e.g., the Catawba, were the Indian stock involved.

Considerable phenotypic variation is found within the isolate today, with extremes of skin color from light to dark and of hair form from very curly to straight- The morphology of the face also suggests broad racial backgrounds. It is therefore of interest to learn what the blood factors and hemoglobins tell of the composition of this population of multiple racial origins.

In 1958, in cooperation with Dr. Amoz Chernoff, blood samples were…

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Human Genetic Diversity and the Nonexistence of Biological Races

Posted in Anthropology, Articles, Health/Medicine/Genetics on 2011-10-07 21:46Z by Steven

Human Genetic Diversity and the Nonexistence of Biological Races

Human Biology
Volume 75, Number 4, August 2003
pages 449-471

Rich Kittles, Associate Professor of Medicine and Epidemiology and Biostatistics
University of Illinois, Chicago

Jeffrey C. Long, Professor of Anthropology
University of New Mexico, Albuquerque

Sewall Wright’s population structure statistic, FST, measured among samples of world populations is often 15% or less. This would indicate that 85% of genetic variation occurs within groups while only 15% can be attributed to allele frequency differences among groups. In this paper, we show that this low value reflects strong biases that result from violating hidden assumptions that define FST. These limitations on FST are demonstrated algebraically and in the context of analyzing dinucleotide repeat allele frequencies for a set of eight loci genotyped in eight human groups and in chimpanzees. In our analyses, estimates of FST fail to identify important variation. For example, when the analysis includes only humans, FST = 0.119, but adding the chimpanzees increases it only a little, FST = 0.183. By relaxing the underlying statistical assumptions, the results for chimpanzees become consistent with common knowledge, and we see a richer pattern of human genetic diversity. Some human groups are far more diverged than would be implied by standard computations of FST, while other groups are much less diverged. We discuss the relevance of these findings to the application of biological race concepts to humans. Four different race concepts are considered: typological, population, taxonomic, and lineage. Surprisingly, a great deal of genetic variation within groups is consistent with each of these concepts. However, none of the race concepts is compatible with the patterns of variation revealed by our analyses.

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Gender Differences in Ancestral Contribution and Admixture in Venezuelan Populations

Posted in Articles, Caribbean/Latin America, Health/Medicine/Genetics, Media Archive on 2011-07-18 20:31Z by Steven

Gender Differences in Ancestral Contribution and Admixture in Venezuelan Populations

Human Biology
Volume 83, Number 3 (June 2011)
pages 345-361
E-ISSN: 1534-6617 Print ISSN: 0018-7143

D. Castro De Guerra
Instituto Venezolano de Investigaciones Científicas

C. Figuera Perez
Instituto Venezolano de Investigaciones Científicas

M. H. Izaguirre
Instituto Venezolano de Investigaciones Científicas

E. Arroyo Barahona
Universidad Central de Venezuela

A. Rodriguez Larralde
Instituto Venezolano de Investigaciones Científicas

M. Vivenes De Lugo
Universidad de Oriente

The origin of the contribution of uniparental heritage were analyzed in 615 samples of individuals proceeding from 13 towns classified according to historic differences in their emergence and development as African-derived, European-derived, and admixed/urban. Mitochondrial and Y-chromosome haplogroups were identified by PCR-restriction fragment length polymorphism. The results were compared with previous estimates of admixture made with autosomal markers and with historic aspects. The results show a predominantly indigenous genetic contribution through the female, being more prevalent in urban populations; the African contribution, although dispersed, presents a larger concentration in the African-derived towns, whereas the European contribution is limited to populations with this origin, reflecting isolation and the conservation of the distribution pattern of genes of the Colonial era. With regard to admixture through males, it is almost exclusively of European origin, whereas the African contribution is basically concentrated in the African-derived towns, and the Amerindian lineages are almost nonexistent. The genome of paternal heredity, as opposed to the autosomal and the mitochondrial, shows a homogeneous pattern of admixture that is independent of the origin of the population studied, suggesting that European genes have been introduced into the Venezuelan population through male immigrations, whereas the indigenous contribution has been preserved in the Venezuelan genetic pool through the women. These results provide evidence of the heterogeneity in the genetic origin of the Venezuelan population, which should be taken into account in forensic and epidemiologic genetic studies.

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