Use the following information to answer the question below.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
In the United States, the parasite that causes malaria is not present, but it is present in African-Americans whose ancestors were from equatorial Africa. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?
A) stabilizing selection; disruptive selection
B) disruptive selection; stabilizing selection
C) directional selection; disruptive selection
D) directional selection; stabilizing selection

Question

Quizplus · Accepted Answer

In the United States, where malaria is not present, the sickle-cell allele should be under directional selection against it, as it provides no advantage and can cause sickle-cell disease. In equatorial Africa, where malaria is prevalent, the sickle-cell allele is maintained by stabilizing selection because heterozygotes have a survival advantage against malaria.

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