Genetic analysis proves that the United States is a "big mix"

In the United States, almost no one can trace back to where their ancestors came from only one place. According to a new study, for many people, their past may be surprising.

Researchers have found that a high percentage of ancestors of African-American, European-American and Latino Americans originate from ethnic groups beyond their self-identity. For example, in general, the African-American genome contains 1/4 of European ancestry; and almost 4% of European-Americans have African ancestry.

Joanna Mountain, a geneticist at 23andMe in Mountain View, Calif., pointed out that until recently, “human population geneticists have always preferred to ignore the United States.” (The company provided genetic testing for this study.)

Mountain said that given its long history of immigration from around the world, the country is "considered to be confused in genetics." However, Mountain and her colleagues believe that they may have an opportunity to decipher Americans' complicated genetic lineages. The secret weapon of the researchers is 23andMe's huge genetic information database.

If a person signs up for 23andMe's genetic analysis project, they can choose whether to use their own data for research. When the Mountain team edited the database for the study, 23andMe had 500,000 customers, and about 80% agreed to use their information for such research. Katarzyna Bryc, the first author of the new paper and human geneticist at 23andMe, points out that this makes the data set used for the study “more than an order of magnitude larger” than the amount of data commonly used to analyze population mix.

Researchers began with the genetic ancestors of the three largest ethnic groups in the United States: European, African, and Latino Americans. These classifications are based on what 23andMe customers have defined themselves. But as one might expect, in a country where hundreds of years of different ethnic groups meet and multiply, the genetic boundaries between races are quite vague.

Bryc explained: “You will see all the different ancestors in one race.” For example, the genome of an African-American generally contains 73.2% of Africans, 24% of Europeans, and 0.8% of Indians. At the same time, Latin Americans have an average of 18% of Indians, 65.1% of Europeans (mainly from the Iberian Peninsula) and 6.2% of Africans.

Researchers reported the results of this study in the online edition of the American Journal of Human Genetics.

Although the average may vary, at least 3.5% of European-Americans have African ancestry. In South Carolina and Louisiana, about 12% of European-Americans have at least 1% of African descent. At the same time in Louisiana, about 8% of European-Americans have at least 1% of Indian ancestors.

Andres Moreno-Estrada, a population geneticist at Stanford University in Palo Alto, Calif., who was not involved in the study, believes that the new study is "a very good job." He said: "Compared to other countries in the Americas, the United States has a very special genetic imprint."

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