28.3: African and European Gene Flow

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The Atlantic Slave Trade took place from the 16th century to the 19th century, and moved about 5 million people from Africa to the Americas. Most African-Americans today have a mixture of 80% African and 20% European heritage. When two parents of different ethnicities have children, their children will inherit one chromosome from each parent, and their grandchildren will inherit chromosomes that are a mosaic of the two ethnicities due to recombination. As time passes, the increasing number of recombination events will decrease the length of the “African” or “European” stretches of DNA.

Recombination events are not spread evenly throughout the chromosomes, but happen at hotspots. African and European DNA have different hot spots, which could be due to differences in the amino acid composition of PRDM9, a histone H3(K4) trimethyltransferase which is essential for meiosis.

Difference in disease succeptibility can be predicted for African and European populations. With se- quencing, this knowledge can also be applied to mixed populations. For example, Africans have a higher risk of prostrate cancer which is directly linked to an area in chromosome 8 that maps to a cancer proto- oncogene[? ]. If a mixed individual has the African sequence in that area, he or she will have the increased risk, but if the individual has the European sequence, he or she will not have an increased risk. The same approach can be applied to breast cancer, colon cancer, multiple sclerosis, and other diseases.