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The Distribution of Ancestry of Self-Reported African Americans across the US
(A) Differences in levels of African ancestry in African Americans (blue). (B) Differences in levels of Native American ancestry in African Americans (orange). (C) Differences in levels of European ancestry of African Americans (red), from each state. States with fewer than ten individuals are excluded in gray. (D) The geographic distribution of self-reported African Americans with Native American ancestry. African Americans in each state with 2% or more Native American ancestry is shown by shade of green. States with fewer than 20 individuals are excluded in gray.
Image Credit: The American Journal of Human Genetics
23andMe sketches USA's genetic portrait
First large-scale nationwide analysis yields maps of genetic ancestry reflecting US history.
23andMe, Inc., a leading personal genetics company, has announced the publication of their study pinpointing fine differences in genetic ancestry of individuals across the United States.
For more than four hundred years ago, the United States has served as a meeting place for people from different continents. This study illuminates how American history and the ongoing mixing of people of African, European, and Native and South American origins can be seen in our DNA.
"The relationship between genomics and historical events can shed light on our understanding of the history of the population of the United States, and the history of our country itself. This study helps us build a bridge between data and the people and events that shaped our nation's history, revising long-held notions of who we are as individuals and as a country. In a unique way, genomics helps put a multicultural face on American history."
Henry Louis Gates, Jr., Director of the Hutchins Center for African and Professor of African American Research at Harvard.
Led by 23andMe population geneticist Dr. Katarzyna Bryc, PhD, the study generates the first dense, state-by-state maps showing the gradients of ancestry within populations of self-identified African Americans, European Americans and Latinos across the United States.
The study leverages samples of 160,000 genetic samples with precise estimates of ancestry to reveal the rate of ancestry mixing among American populations, and where it has occurred geographically:
All three 1) African Americans, 2) European Americans and 3) Latinos - are from Africa, Europe and the Americas combined. The ancestry proportions point to the different regional impacts of slavery, immigration, migration and colonization within the United States:
• Approximately 3.5 percent of European Americans have one percent or more African ancestry. Many of these European Americans who describe themselves as "white" may be unaware of their African ancestry since the African ancestor may be five to 10 generations in the past. European Americans with African ancestry are found at much higher frequencies in southern states than in other parts of the United States.
• The highest levels of African ancestry among self-reported African Americans are found in southern states, especially South Carolina and Georgia. One in every 20 African Americans carries Native American ancestry. More than 14 percent of African Americans from Oklahoma carry at least two percent Native American ancestry, likely reflecting the Trail of Tears migration following the Indian Removal Act of 1830.
• Among self-reported Latinos in the United States, those from states in the southwest, especially from states bordering Mexico, have the highest levels of Native American ancestry.
All three groups - African Americans, European Americans and Latinos - showed asymmetrical male and female ancestry contributions, with more European male and more Native American and African female ancestors. This asymmetry is likely a legacy of slavery, unbalanced sex ratios in frontier settings, as well as other social factors in early US history.
The study, entitled "The genetic ancestry of African, Latino, and European Americans across the United States," was published on December 18, 2014 in the American Journal of Human Genetics.
"We show that the signatures of recent historical migrations can be seen in the DNA of present-day Americans. Furthermore, our results can inform the design of medical genetic studies. For example, the presence of Native American and African ancestry in European Americans may have implications for genetic studies of complex diseases."
Katarzyna Bryc PhD, Research Fellow in Genetics, Department of Genetics, Harvard Medical School, Boston, Massachusetts
The study also gives insight on the long-open question of how genetic ancestry aligns with self-reported identities. For example, the authors found those with as much as 28 percent African ancestry are more likely to describe themselves as European American than as African American, whereas individuals with more than 30 percent African ancestry are more likely to describe themselves as African-American.
This study, made possible by data contributed by more than 160,000 23andMe customers*, makes it clear that the legacy of historical interactions between Native Americans, Europeans, and Africans is visible in the DNA of present-day Americans.
Over the past 500 years, North America has been the site of ongoing mixing of Native Americans, European settlers, and Africans (brought largely by the trans-Atlantic slave trade), shaping the early history of what became the United States. We studied the genetic ancestry of 5,269 self-described African Americans, 8,663 Latinos, and 148,789 European Americans who are 23andMe customers and show that the legacy of these historical interactions is visible in the genetic ancestry of present-day Americans. We document pervasive mixed ancestry and asymmetrical male and female ancestry contributions in all groups studied. We show that regional ancestry differences reflect historical events, such as early Spanish colonization, waves of immigration from many regions of Europe, and forced relocation of Native Americans within the US. This study sheds light on the fine-scale differences in ancestry within and across the United States and informs our understanding of the relationship between racial and ethnic identities and genetic ancestry.
*Data was contributed by 23andMe customers who provided informed consent to take part in this research under a protocol approved by the AAHRPP-accredited institutional review board, Ethical and Independent Review Services.
This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).
23andMe, Inc. is the leading personal genetics company dedicated to helping people access, understand and benefit from the human genome. The vision for 23andMe is to personalize healthcare by making and supporting meaningful discoveries through genetic research. 23andMe, Inc., was founded in 2006, and the company is advised by a group of renowned experts in the fields of human genetics, bioinformatics and computer science. More information is available at http://www.23andme.com.
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