Why Is the Incidence of Sickle-Cell Anemia an Excellent Example

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The Answer is Homozygous normal individuals have healthy red blood cells (and hence normal oxygen distribution to tissues)but are susceptible to malaria.Homozygous abnormal individuals display sickle-cell anemia,a very serious disease that usually results in death before reproductive age.Those who are heterozygous are more fit in malarial environments,because they display only very mild symptoms of sickle-cell anemia (if any)and are much less susceptible to malaria.Hence the sickle-cell allele is maintained in fairly high frequencies in regions where malaria is common.There is a tradeoff between a positive effect and a negative effect,so a trait that from one point of view should be selected against is maintained because,from a different point of view,it is also selected for.

Why Is the Incidence of Sickle-Cell Anemia an Excellent Example

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