Thursday, December 18, 2014

The average African-American genome is nearly a quarter European while less than 4% of European Americans carry African ancestry

The average African-American genome is 73.2% African, 24% European, and 0.8% Native American. Latinos carry an average of 18% Native American ancestry, 65.1% European ancestry (mostly from the Iberian Peninsula), and 6.2% African ancestry. Latinos with the highest proportion of African ancestry (about 20%) are from Louisiana, followed by states such as Georgia, North Carolina, New York, and Pennsylvania. In Tennessee and Kentucky, Latinos tend to have high proportions of European ancestry. And in the Southwest, where states share a border with Mexico, Latinos tend to have higher proportions of Native American ancestry. At least 3.5% of European Americans carry African ancestry, though the averages vary significantly by state. European Americans with African ancestry are found at much higher frequencies in southern states than in other parts of the United States. In South Carolina and Louisiana, about 12% of European Americans have at least 1% African ancestry. In Louisiana, too, about 8% of European Americans carry at least 1% Native American ancestry. Oklahoma is the state where the most African-Americans have significant Native American ancestry. More than 14% of African Americans from Oklahoma carry at least 2% Native American ancestry. One way that history shows up in contemporary genomes is in what researchers call a sex bias. By looking at the kinds of DNA that are passed down only by mothers, they can calculate how many of a person’s ancestors from each population were male and female. In all three populations, they found the same signal: European ancestors tended to be male, while African and Native American ancestors tended to be female. Researchers found that those with as much as 28% African ancestry were more likely to describe themselves as European American than as African American, whereas individuals with more than 30% African ancestry were more likely to describe themselves as African-American. Individuals with just 5% Native American ancestry usually called themselves Latino. European Americans are the least admixed group, with 98.6% European ancestry, 0.19% African ancestry, and 0.18% Native American ancestry on average. Scandinavian ancestry is found in trace proportions in most states but comprises about 10% of ancestry in European Americans living in Minnesota and the Dakotas.

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