An assessment of genomic diversity in the United States of America clarifies the role of pre-Civil War admixture and early 20th century transit routes in shaping the migration history and genomic diversity among African-Americans communities. The new study, by Simon Gravel of McGill University and colleagues, will publish on May 27, 2016 in PLOS Genetics.

In the Great Migration, six million African Americans moved from the rural Southern United States to the urban Northeast, Midwest, and West between 1910 and 1970, to seek better social and economic opportunities. This migration had a profound impact on African-American communities and also on their nation-wide genomic diversity. In the current study, scientists used genetic data from 3,726 African-Americans from across the U.S. to estimate patterns of ancestry. They report that 82.1% of African-Americans' ancestors resided in Africa prior to the advent of transatlantic travel, while 16.7% lived in Europe and 1.2% in the Americas. They find that African-Americans living in the southern U.S. have a greater percentage of African ancestry than those in the North or West and that individuals with higher European ancestry were more likely to migrate to the North and West, reinforcing regional differences in ancestry.

The study's detailed approach to the analysis of African American genetics confirms previous findings and fills in details of African American heritage that may be absent from the historical record. As researchers seek to increase the representation of African-Americans in medical genetic studies and reduce health disparities, this study will facilitate the design and analysis of nation-wide representative cohorts.