DNA and genealogical information from over 700,000 American individuals paint a detailed picture of the subtle patterns of migration and settlement in post-colonial USA. The analysis, published online in Nature Communications this week, shows levels of population structure, shaped by many different geographical and cultural factors, which have previously been difficult to determine.

The pre-colonial populations of North America have been quite well studied but the more recent population structure is less easy to assess. Catherine Ball and colleagues analysed the DNA of 770,000 individuals originating in the USA, and included user-generated genealogical data to help put together a network of their relationships. They found genetic signatures of pre-immigration ancestry, such as clusters of Scandinavian and Finnish ancestry (who moved to the USA within the past 150-200 years) in the Midwest. The data also depict movements and settlements across east-west and north-south gradients, and pick out groups who remained isolated after moving to the USA, for geographical or cultural reasons, such as Amish populations within Midwestern states and Pennsylvania.

In addition to revealing demographic insights into population structure changes of North America after European settlement, the study also identifies patterns in clusters of gene variants associated with various diseases. However, a more comprehensive examination of disease-related genetic variation is needed to provide clinically relevant insights into fine-scale patterns of genetic disease risk in this population.