The dna testing/analysis company 23&me released some findings from their 160000+ dna sample collection-
Black ppl tested in the study are ~25% white
10% of whites in S Carolina & Louisiana are at least "one drop black"
28% is the tipping point of African genes where, above that, biracial ppl identify as black. Below that, most consider themselves white


~~~~~~OVerall-
On average, the scientists found, people who identified as African-American had genes that were only 73.2 percent African. European genes accounted for 24 percent of their DNA, while .8 percent came from Native Americans.

Latinos, on the other hand, had genes that were on average 65.1 percent European, 18 percent Native American, and 6.2 percent African. The researchers found that European-Americans had genomes that were on average 98.6 percent European, .19 percent African, and .18 Native American.

These broad estimates masked wide variation among individuals. Based on their sample, the resarchers estimated that over six million European-Americans have some African ancestry. As many as five million have genomes that are at least 1 percent Native American in origin. One in five African-Americans, too, has Native American roots.

Dr. Mountain and her colleagues also looked at how ancestry might influence ethnic identification.

Most Americans with less than 28 percent African-American ancestry say they are white, the researchers found. Above that threshold, people tended to describe themselves as African-American.

Katarzyna Bryc, a 23andMe researcher and co-author of the new study, didn’t want to speculate about why people’s sense of ethnic identity pivots at that point.

“We can only take it so far as geneticists,” she said.

The scientists also linked geographical patterns to their subjects’ ancestries. Latinos in the Southwest had high levels of Native American DNA, they found, while Latinos in the Southeast had high levels of African DNA.

The genes of African-Americans varied strikingly from state to state. In Oklahoma, the researchers estimated, 14 percent of African-Americans have genomes that are at least 2 percent Native American. This high percentage is probably due to the unique history of the state.

Some Native American tribes in the South, such as the Cherokee and Choctaw, kept African slaves. When they were expelled to Oklahoma in the 1830s, they brought the slaves with them. In some tribes, Native Americans and African slaves intermarried, and their descendants continue to live in Oklahoma today.

Dr. Saunt was fascinated in particular by the genetic findings among people in South Carolina. Dr. Mountain and her colleagues estimated that 13.3 percent of European-Americans in South Carolina have genes that are at least 1 percent African in origin.

At one point, Dr. Saunt noted, the percentage of South Carolina residents who were slaves was greater than in any other state. But there was also a large population of freed slaves in Charleston permitted to interact with whites.

“We know lots of planters had mistresses in Charleston, and they obviously had children together,” said Dr. Saunt. “So what happened to those children? Some remained in the African-American community, and some moved into the white community when they were able to.”

Jeffrey C. Long, an anthropologist at the University of New Mexico who was not involved in the study, cautioned that the research was not based on a random sample of Americans. Instead, Dr. Mountain and her colleagues studied only people who were curious enough about their DNA to pay for a test.

“Perhaps people who have mixed ancestry are more interested in their ancestry than people who don’t think they have mixed ancestry,” Dr. Long said.

David Reich, a geneticist at Harvard University and a co-author on the new study, acknowledged this was a reasonable concern. “It’s classic survey bias,” he said. But Dr. Reich also noted that the new results were consistent with smaller studies done in the past.

As genetic databases grow, Dr. Reich predicted it would be possible to get even more detailed insights into American history. DNA may be able to illuminate the movements of people across the United States, such as the Great Migration that took African-Americans from the South to Chicago.

http://mobile.nytimes.com/2014/12/25/science/23andme-genetic-ethnicity-study.html?_r=0