Balancing selection

Polymorphism is the phenomenon in genetics that several different variants ( alleles) are found in a significant proportion of a characteristic in a population.

This is important insofar as each feature is exposed to in its environment a selection and it would be equally possible that only a model with maximum fitness interspersed in evolution. The limit a share of 95 % or even 99 % is often set, the must not exceed the most common version. A balanced polymorphism then occurs when both variants have an evolutionary advantage, so that both variants represent a distinct survival strategy, and not a variant of the other is clearly superior.

Example of a balanced polymorphism is the increased occurrence of sickle cell anemia in Africa. In this " genetic disease ", the erythrocytes are distorted crescent- shaped, which causes many health drawbacks - but individuals can with a heterozygous constitution for the disease-causing gene have a survival advantage, because with this feature is accompanied by a resistance to malaria. In areas where malaria is therefore creating a balanced polymorphism in relation to malaria relatively protected anemia patients and the malaria -prone healthy subjects.

• Genetics
• Population Genetics