Genetic variants found in a significant proportion of the population (usually 1% of people) that may or may not be associated with disease. An association, however, does not necessarily mean that it is the cause of disease.
Use in clinical context
Many sites in the genome are polymorphic. While not all have functional implications, there are many that do.
Blood groups are determined by proteins expressed on the outside of red blood cells. These proteins are encoded for by polymorphic genes, meaning different people have different variants of the genes and so express different proteins. The different blood groups influence blood clotting which may have conferred evolutionary advantages, and they may also influence the effectiveness of response to infections. In modern medicine blood groups are a greater consideration in blood donation. An individual’s immune system ignores blood of its own group. However, if an individual is given blood from a donor with a different group, their immune system recognises the different proteins on the outside of the donated blood cells and initiates an immune response.