In central Africa, the frequency of the sickle-cell allele has remained stable over the years because the allele protects against malaria. In the United States, malaria was eradicated by eliminating the mosquito that spreads the disease. The decreasing frequency of the sickle-cell allele in African Americans since malaria was eliminated in the United States is an example of
A) stabilizing selection.
B) the founder effect.
C) directional selection.
D) genetic drift.
E) disruptive selection.

Question

Quizplus · Accepted Answer

Directional selection occurs when an environmental change favors a specific phenotype over others, leading to a shift in allele frequency in the population. In this case, the decrease in the sickle-cell allele frequency among African Americans after the eradication of malaria in the United States is an example of directional selection, as the protective advantage of the sickle-cell allele against malaria is no longer beneficial, leading to a decrease in its frequency.

In Central Africa, the Frequency of the Sickle-Cell Allele Has