page_title: Race and genetics
section_title: Analysis of blood proteins
hierarchical_section_title: Race and genetics / Research methods / Trait, protein and gene studies / Analysis of blood proteins
caption_attribution_description: English: based on diagrams from http://anthro.palomar.edu/vary/vary_3.htm
context_page_description: The relationship between race and genetics is relevant to the controversy concerning race classification. In everyday life, many societies classify populations into groups based on phenotypical traits and impressions of probable geographic ancestry and cultural identity—these are the groups usually called "races" in countries like the United States, Brazil, and South Africa. Patterns of variation of human genetic traits are generally clinal, with more abrupt shifts at places where steady gene flow is interrupted. The pattern of genetic variants tend to form larger regional clusters. Such a pattern can be explained by the expansion of the human population from Africa and serial genetic bottlenecks. This causes genetic clusters to correlate statistically with population groups when a number of alleles are evaluated.
  Genetic analysis enables scientists to estimate the geographic ancestry of a person by using ancestry-informative markers, and by inference the probable racial category into which they will be classified in a given society. In that way there is a distinct statistical correlation between gene frequencies and racial categories.
context_section_description: Before the discovery of DNA, scientists used blood proteins (the human blood group systems) to study human genetic variation. Research by Ludwik and Hanka Herschfeld during World War I found that the incidence of blood groups A and B differed by region; for example, among Europeans 15 percent were group B and 40 percent group A. Eastern Europeans and Russians had a higher incidence of group B; people from India had the greatest incidence. The Herschfelds concluded that humans comprised two "biochemical races", originating separately. It was hypothesized that these two races later mixed, resulting in the patterns of groups A and B. This was one of the first theories of racial differences to include the idea that human variation did not correlate with genetic variation. It was expected that groups with similar proportions of blood groups would be more closely related, but instead it was often found that groups separated by great distances (such as those from Madagascar and Russia), had similar incidences. It was later discovered that the ABO blood group system is not just common to humans, but shared with other primates, and likely predates all human groups.
caption: Geographic distribution of blood group A
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