What is "balanced polymorphism?

What is balanced polymorphism?

• Answer:

  Balanced Polymorphism In regions of the world (e.g., parts of Africa) where malaria caused by Plasmodium falciparum is common, the allele for sickle-cell hemoglobin is also common. This is because children who inherit •one gene for the "normal" beta chain of hemoglobin and •one sickle gene are more likely to survive than either homozygote. •Children homozygous for the sickle allele die young from sickle-cell disease but •children homozygous for the "normal" beta chain are more susceptible to illness and death from falciparum malaria than are heterozygotes. Hence the relatively high frequency of the allele in malarial regions. When natural selection favors heterozygotes over both homozygotes, the result is balanced polymorphism. It accounts for the persistence of an allele even though it is deleterious when homozygous