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Genetic variation between humans can be ascribed to differences between individuals within populations (85-90%) and to differences between populations (10-15%). As humans migrated out of Africa, they adapted to new environments and groups became isolated from one another. This resulted in different frequencies of genetic variants in the resultant populations.

Evidence from mitochondrial DNA and Y-chromosome studies shows that the San of Southern Africa are likely to be the oldest human population group. We have participated in a collaboration with researchers from the USA to collect samples from this population group for genome-wide analysis, which will be an important resource for gaining insight into the genetic history of humans.

Admixture occurs when two or more previously separated population groups produce offspring. The predominant population group in the Western Cape, South Africa, is the admixed group known officially as the South African Coloured (SAC). The SAC had their origins in the diverse groups in the early days of Cape history, including Europeans settlers, the slaves they brought in from Indonesia, India and other parts of Africa, local Bantu-speakers, and the indigenous Khoe-San. They therefore constitute a complex combination of continental populations.

We are using the powerful technique of admixture mapping to find genetic variants that differ in frequency between source populations of the SAC and may have a role in susceptibility to tuberculosis.

In addition, proportions of ancestry received from source populations vary between individuals in the population and this may have a confounding effect in genetic association studies if the differences are not homogeneous between case and control groups. We have therefore also developed a small panel of ancestry informative markers (AIMs) that can be used to adjust for admixture in candidate gene association studies of the SAC – see Software.