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Sickle-Cell Anemia

The text notes that an alternate allele of the hemoglobin gene can cause sickle-cell anemia when a person is homozygous for this allele, but that a person who is heterozygous for the allele actually can derive a benefit from it--protection from malaria. In the United States, 8 percent of African Americans are carriers for the sickle-cell allele, while in central Africa the figure is 20 percent. What could account for this difference? Assess.

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The standard evolutionary explanation is that since the apparent benefit of having the sickle-cell allele is practically non-existent in America, the allele has decreased in the gene pool. In other words, why have the mutant allele ...