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Thread: The genetic ancestry of African, Latino, and European Americans (23andme study)

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    The genetic ancestry of African, Latino, and European Americans (23andme study)

    Don't think this has been posted yet? Pretty large sample size

    Link to paper
    Link to supplement

    The genetic ancestry of African, Latino, and European Americans across the United States.

    Katarzyna Bryc, Eric Durand, J Michael Macpherson, David Reich, Joanna Mountain

    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.

    I'm just going to post some quotes/charts i found particularly interesting but there's much more if you read the whole paper/supplement.


    *************AFRICAN AMERICANS**********************

    Much was known already but still nice to see confirmation, good to keep in mind though that despite the huge sample size there might still be some sampling bias as also pointed out by the authors themselves. Also there's always individual variation, shown clearly in the distribution graphs.

    Genome-wide ancestry estimates of African Americans show average proportions of 73.2% African, 24.0% European, and 0.75% Native American ancestry.

    Unlike previous estimates of the mean proportion of African ancestry, which typically have ranged from 77% to 93% Africanancestry our estimates, depending on exclusions, are 73% or 75%. There are several possible explanations for our low mean African ancestry. If our ancestry composition estimates are were downward biased, then the African Americans may have similar levels of African ancestry consistent with other studies, and our results are simply underestimates. However, our ancestry composition estimates are extremely well calibrated for African Americans from the 1000 Genomes Project and their consensus estimates, and see no evidence of a downward bias

    Even excluding individuals with no African ancestry, which are likely the result of survey errors, we still estimate a higher European, and corresponding lower African, mean genetic ancestry proportion in 23andMe African Americans compared to previous studies of African Americans. A significant difference between the 23andMe cohort of African Americans and many groups previously studied is geographic sampling location. Our cohort reflects heavier sampling from California and New York, likely driven by population density as well as awareness of genetic testing or 23andMe. Both are regions where African Americans have lower mean African ancestry than other studies of African Americans, which are often drawn from locations in the South. However, participation in 23andMe is not free and requires online access, therefore it is important to note that other social, cultural, or economic factors may interact to affect ancestry proportions of those individuals who choose to participate in 23andMe.

    Notice there's a few self-identified African Americans with African ancestry being as low as 0-2%! I'm guessing there might also be some biracials included. On the other end the range also includes people of "pure" African ancestry in between 98-100%!









    On average the highest levels of African ancestry are found in African Americans from the South, especially South Carolina and Georgia(Figure 1A). We find lower proportions of African ancestry in the Northeast, the Midwest, the Pacific Northwest and California.












    Though mean estimates of Native American ancestry are low, many African Americans carry detectable levels of Native American ancestry. Over 5% of African Americans are estimated to carry at least 2% Native American ancestry genome-wide... Using a lower threshold of 1% Native American ancestry, we estimate that about 22% of African Americans carry some Native American ancestry, which implies that more than 1 in 5 African Americans may have a Native American ancestor in their genealogy within the last 11 generations.

    Oklahoma shows the highest proportion of African Americans with substantial Native American ancestry, where over 14% of African Americans from Oklahoma carry at least 2% Native American ancestry.




    This is probably the most surprising finding of the study and may also have implications on how African American feel about their minor European admixture.


    A sex bias in African American ancestry, with greater male European and female Africancontributions, has been suggested through mtDNA, Y chromosome, and autosomal studies. Through comparison of estimates of X chromosome and genome-wide African and European ancestry proportions, we estimate that approximately 6% of ancestors of African Americans were European females, while 19% were European males. On average across African Americans, we estimate that the X chromosome has a 5% increase in African ancestry and 18% reduction in European ancestry relative to genome-wide estimates (see Table 1). Sex bias in ancestry contributions may have been driven by unbalanced sex ratios in immigration frontier settings, exploitation, or other social factors.


    We find that our estimates of sex bias in ancestry contributions in African Americans, withgreater male European ancestry and greater female African contributions, support over three times as many European male ancestors as female European ancestors in African Americans. Sex bias in ancestry contributions has been suggested to stem from interactions with male European slave-owners and female African slaves. However, our estimates of admixture dates, with a mean admixture date of 4 generations, implies that the majority of admixture events between Europeans and African ancestry has taken place much more recently than 1865, and in particular, may have taken place after slavery. Taken together, these datapoints suggest that sex biased admixture may also reflect post-slavery social and cultural influences.





    *************EUROPEAN AMERICANS**********************

    Interesting outcomes, seem to correlate with known migration patterns pretty well and also the current self-identification of migrant origins among European Americans as shown in this map


    Inferred British/Irish ancestry is found in European Americans from all states at mean proportions of above 20%, and represents a majority of ancestry, above 50% mean proportion, in states such as Missisippi, Arkansas, and Tennessee. We note that these states are similarly highlighted in the map of the self-reported “American” ethnicity in the US census survey1, which may reflect regions with lower subsequent migration from other parts of Europe.


    Inferred Eastern European ancestry is found at its highest levels in Illinois, Michigan, and Pennsylvania, potentially stemming from immigration during the late 19th and early 20th centuries, settling in metropolitan areas in the Northeast and Midwest.

    Inferred Iberian ancestry, found overall at lower mean proportions, still represents a measurable ancestry component in Florida, Louisiana, California, and Nevada, and may point to the early Spanish rule and colonization of the Americas.

    Scandinavian ancestry in European Americans is highly localized; most states show only trace mean proportions of Scandinavian ancestry, while it comprises a significant proportion, upwards of 10%, of ancestry in European Americans from Minnesota and the Dakotas.












    Non-European admixture is detectable for only a small minority and seems to be at lower %'s than reported in previous studies

    Though the majority of European Americans in our study did not carry Native American or African ancestry, even a small proportion of this large population that carry non-European ancestry translates into millions of European Americans who carry African and Native American ancestry. Our results suggest that the early US history, beginning in the 17th century (or around 12 generations ago), may have been a time of many population interactions resulting in admixture.
    Applying these estimates to self-reported ethnicity data from the 2010 US Census suggests that over 6 million Americans, who self-identify as European, may carry African ancestry. Likewise, as many as 5 million Americans who self-identify as European may have at least 1% NativeAmerican ancestry.
    Though the average levels of Native American ancestry are trace, if we examine the frequency with which European Americans carry at least 2% Native American ancestry, we see that Native American ancestry occurs most frequently in Louisiana, North Dakota, and other states in the West. We estimate that 4% of self-reported European Americans living in Louisiana and North Dakota carry segments of Native American ancestry.
    We estimate that a substantial fraction, at least 1.4%, of self-reported European Americansin the US carry at least 2% African ancestry. Using a less conservative threshold, approximately 3.5% of European Americans have 1% or more African ancestry (Figure S9). Consistent with previous anecdotal results, the frequency of European American individuals who carry African ancestry varies strongly by state and region of the US (Figure 3A). In particular, individuals with African ancestry are found at much higher frequencies in states in the South than in other parts of the US: about 5% of self-reported European Americans living in South Carolina and Louisiana have at least 2% African ancestry. Lowering the threshold to at least 1% African ancestry (potentially arising from one African genealogical ancestor within the last 11 generations), European Americans with African ancestry comprise as much as 12% of European Americans from Louisiana and South Carolina and about 1 in 10 individuals in other parts of the South (Figure S9).






    *************LATINO AMERICANS**********************


    Not much text on them but this quote seems to suggest they didn't find any strictly Zambo (Amerindian/African mixed) persons among their samples.

    Latinos encompass nearly all possible combinations of African, Native American, and European ancestries, with the exception of individuals who have a mix of African and Native American ancestry without European ancestry.

    This map seems to make sense given the concentration of Carribean Hispanics on the East Coast and mostly Mexicans on the West Coast and along the border. But not sure why Lousiana seems to have Latino's with the highest African %'s.





    This is a very useful breakdown according to nationality as of course Latino's are not a single ethnicity. In fact each population is showing up as triracial to some degree but of course in varying proportions. Also fascinating how the selfidentified black Latino's actually are showing an average African ancestral contribution below 50%! Would have been nice if they had provided some more stats though like minimum and maximum value for each component to give a better indication of the range.


    Last edited by Don Felipe; 10-06-2014 at 10:05 PM.

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    In order to check how significant Amerindian & African admixture levels among European Americans might be they also compared with results for about 15.000 selfidentified (4GP) Europeans among their client database. When excluding Spain, Portugal and a couple of other countries it's hardly detectable though. They also found 21 Amerindian maternal haplogroups among their European samples But most of them in Spain.

    To this end, we generated a cohort of 15, 289 23andMe customers who reported that all four of their grandparents were born in the same European country. The use of four grandparent birth-country has been utilized as a proxy for assessing ancestry, see for example 78, 79. We then examined ancestry composition results for these individuals, and calculated how at what rate we detected at least 1% African and at least 1% Native American ancestry. Overall, we find very low levels of African and Native ancestry, with 0.98% of Europeans showing African ancestry, and 0.26% of Europeans carry Native American ancestry. These levels are substantially lower than the 3.5% and 2.7% of European Americans that carry African and Native American ancestry, respectively.
    Excluding countries that had major and minor ports in the Atlantic with strong connections to the slave trade (namely, Portugal, Spain, France, United Kingdom) and Malta, which has been the site of migrations from Africa and the Middle East (from Phoenicia and Carthage) and served as a major port since the completion of the Suez Canal. Excluding these countries, we obtain a dataset of 9, 701 Europeans, where we find African and Native American ancestry is virtually absent, with only 0.04% of individuals carrying 1% or more African ancestry, and 0.01% carrying 1% or more Native American ancestry, within the margins of survey error estimates
    We find that the frequency of Native American haplogroups correlates with our estimates of genome-wide ancestry in European Americans and African Americans, and are found at appreciable fractions of individuals who are estimated to carry Native American ancestry. The frequencies of aplogroups are shown in Table S7. Furthermore, these haplogroups are virtually absent in individuals with four grandparents from a European country (21 individuals out of 15,651). Furthermore, the majority of these haplogroups are found in individuals from Spain, suggesting the possibility of geneflow returning from the Americas into Spain, which may also be reponsible for driving higher levels of genetic diversity in Europeans from the Iberian peninsula. Excluding Spain, overall Native American specific haplogroups are detected in less than 0.05% of individuals with four grandparents from Europe

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    I like being able to see my state of Pennsylvania has some of the highest percentages of my known ancestry.

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    Interesting that 50 million Americans claim mostly German ancestry, but the average German admixture is quite small when compared to British an Iriish

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    Quote Originally Posted by Pfeifer View Post
    Interesting that 50 million Americans claim mostly German ancestry, but the average German admixture is quite small when compared to British an Iriish
    Most of the English immigration to America was 12-14 generations back, whereas immigration from many other countries, including much of the German was much more recent. The main foundation of the US population was English, thanks to the big head start - a founder effect if you will. The others were more recent, more readily documented, more readily remembered, and thus self-reported on census forms. Back when it was easy to query ftdna and ysearch databases the English to german ratio of ydna origins was something like 5 to 1. Genealogists tend to know their ancestry back more than 2 or 3 generations. The vast majority of folk don't. I have a German great grandmother by the way, but this German ancestry business is a canard.

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    The latino ancestry is skewed to more european ancestry. 23 and me mostly has people from wealthier backgrounds, thus people with more european ancestry take them. For latin America its hard to get proper representitive samples, due to the genetic diversity. THere is no way the average central american is predominantly european.

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    Quote Originally Posted by Rick View Post
    Most of the English immigration to America was 12-14 generations back, whereas immigration from many other countries, including much of the German was much more recent. The main foundation of the US population was English, thanks to the big head start - a founder effect if you will. The others were more recent, more readily documented, more readily remembered, and thus self-reported on census forms. Back when it was easy to query ftdna and ysearch databases the English to german ratio of ydna origins was something like 5 to 1. Genealogists tend to know their ancestry back more than 2 or 3 generations. The vast majority of folk don't. I have a German great grandmother by the way, but this German ancestry business is a canard.
    Yes, altough the Germans had an important contribution to the Us nation as well.

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    Agreed....

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    Quote Originally Posted by tamilgangster View Post
    The latino ancestry is skewed to more european ancestry. 23 and me mostly has people from wealthier backgrounds, thus people with more european ancestry take them. For latin America its hard to get proper representitive samples, due to the genetic diversity. THere is no way the average central american is predominantly european.
    Which shouldn't come as a surprise and is actually mentioned as a possible reason in the text. It's no coincidence that every group mentioned has a greater European mean, though another possibility is that something is wrong with the method. That seems unlikely though, as 23andme has made revisions in the past, and as far as African admixture is concerned, it has gotten much better. I trust 23andme more than the other tests, though I do like parts of the Genographic Project's test.

    Also, I'd bet money that the majority of biracials, or at least a good portion, claim black and fall within the African American category. It seems unlikely that that many black Americans would be 50% African. That degree of admixture is very apparent and I wouldn't say it's as common as what is truly representative of the population here in the mid-Atlantic.
    Last edited by xKeleix; 03-30-2015 at 12:51 AM.
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    Quote Originally Posted by Pfeifer View Post
    Interesting that 50 million Americans claim mostly German ancestry, but the average German admixture is quite small when compared to British an Irish
    According to the United States Historical Census Data Base-USHCDB (2002),
    Populations in the American Colonies of 1775
    Ancestry Percentage
    English 48.7%
    African 20.0%
    Scots-Irish 7.8 %
    German 6.9%
    Scottish 6.6 %
    Dutch 2.7%
    French 1.4%
    Swedish 0.6%
    Other 5.3%
    Note - If the Scottish and Ulster Scots
    (known as Scotch-Irish) are added together they form 14.4%.
    Estimated origin - 1790 United States Census
    European American Ancestry only Percentage
    English 60.9%
    Scots-Irish/Scottish 14.3%
    German 8.7%
    Dutch/French/Swedish 5.4%
    Irish 3.7%
    Unidentifiable 7.0 %
    Total 100%
    African Americans were some 19.3% of the total U.S population.
    Last edited by MitchellSince1893; 03-30-2015 at 01:17 AM.
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