Human genetic variation is often biologically relevant, particularly when it influences (or is influenced by) health outcomes. For example, human genetic variation can modulate disease aetiology as in the case ofhomozygous beta sickle gene (βS/βS or sickle cell) pathology. Conversely, health outcomes, such as the frequency and duration of homozygous sickle cell pathology, can change affected group gene frequencies by selectively targeting and culling specific genotypes in a group, such as clinically more severe βS Bantu/βS Bantu versions of the βS gene, thereby changing future patterns of genetic variation in this gene.
Collier Jackson, Fatimah Linda, "Human genetic variation and health: New assessment approaches based on ethnogenetic layering" (2004). Department of Biology Faculty Publications. 108.