Balanced polymorphism

In genetics, polymorphism is understood to mean the phenomenon that a significant proportion of several different variants ( alleles ) of a trait can be found in a population .

This is important insofar as every feature in its environment is subject to selection and it would also be possible that only one variant with maximum fitness prevails in evolution . A percentage of 95% or even 99% is often set as the limit value, which the most common version must not exceed. A balanced polymorphism occurs when both variants have an evolutionary advantage, so that both variants represent an independent survival strategy and neither variant is clearly superior to the other.

An example of a balanced polymorphism is the frequent occurrence of sickle cell anemia in Africa . In this hereditary disease , the erythrocytes are sickle-shaped, which has many health disadvantages - however, individuals with a heterozygous constitution can have a survival advantage for the disease-causing gene, as this characteristic is associated with resistance to malaria . In malaria areas, a balanced polymorphism arises in relation to those suffering from anemia who are relatively protected from malaria and healthy people susceptible to malaria .