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 the sickle cell allele is present in many African-Americans whose ancestors were from equatorial Africa. Which of the following processes are most likely acting on the sickle-cell allele in the United States, and in equatorial Africa?

Question

Quizplus · Accepted Answer

In equatorial Africa, the sickle-cell allele provides a selective advantage against malaria, leading to stabilizing selection where both normal and sickle-cell alleles are maintained in the population. In the United States, without the pressure of malaria, the sickle-cell allele may be selected against due to its associated health risks, indicating directional selection towards the normal allele.

In Those Parts of Equatorial Africa Where the Malaria Parasite