Scientists have concluded their years of research, in which they were studying the DNA of African Americans, to see how genetic changes add to the risk of disease. They have created the world’s most detailed genetic map as a conclusion of their research. The study has been published in this week’s Nature.

David Reich, an associate member of the Broad Institute of MIT and Harvard, and his colleagues developed the map, after studying the DNA of 30,000 African and Americans. Researchers analyzed the unique DNA of unrelated Africans and Americans of Western African and European lineage, to sketch how precise spots in the genome changed across population groups.

The team has found that on an average, the African-American genome is about 80% African lineage and 20% of European ancestry. For this they used a computational technique called HapMix, which acts like a sieve. They sifted through the genome, to know that either chromosome were from African individual or a European.

These switch points were known as recombination hotspots, which occur in particular places on chromosomes and could be identified as of European and African ancestry. Mapping on this finely tuned scale, the researchers identified about 2,500 recombination hotspots that were active in people of West African lineage but nearly inactive in Europeans.