https://www.vox.com/2014/12/22/7431391/guess-where-white-americans-have-the-most-african-ancestry

> In South Carolina and Louisiana — the states shaded the darkest green on the map above — researchers found that one in 20 people who called themselves white had at least 2 percent African ancestry. And in a lot of the South, about 10 percent of people who identified as white turned out to have African DNA.

...

> Just like white people in the South had the most African ancestry, so did black people.

https://www.science.org/content/article/genetic-study-reveals-surprising-ancestry-many-americans

> The average African-American genome, for example, is nearly a quarter European, and almost 4% of European Americans carry African ancestry.