A team including Gil McVean, Oliver Venn and Peter Donnelly of the WTCHG has identified multiple genetic variants common to humans and their closest living relative, the chimpanzee. Analysis suggests that these variants existed in a common ancestor, before the two species diverged between 5 and 7 million years ago. The conservation of these variants over such a long period suggests that they have been maintained through selection, possibly because they confer resistance to infection by parasites or other pathogens.
Although humans are genetically diverse, almost all variation found in modern populations arose since the split of the human and chimpanzee lineages. Until recently, there were only two known exceptions to this; the classical major histocompatibility (MHC) alleles, which enable the body to recognise and reject foreign tissues, and the ABO blood group locus, which affects proteins on the surface of red blood cells. In both cases, some alleles are shared between humans and other primates. Such long-term maintenance of genetic variation was, however, thought to be extremely rare.
But in a study just published in Science, the WTCHG scientists and their colleagues in Molly Przeworski’s group at the University of Chicago have identified 125 regions where specific combinations of genetic variants, or haplotypes, are shared between humans and chimpanzees. Intriguingly, these are almost all in regulatory regions; several of them apparently affect additional genes involved in determining blood types, as well as other proteins that are likely to affect how human cells interact with key pathogens such as malarial parasites.
‘These findings show the power of host-pathogen warfare for shaping genetic variation’, says Professor McVean, ‘and identify many regions that are likely to affect human resistance to infectious disease.’