In Humans, Sickle-Cell Anemia Is Caused by an Allele That

In humans, sickle-cell anemia is caused by an allele that results in abnormal hemoglobin that sickles red blood cells in certain situations. Individuals who are heterozygous for normal and sickle-cell alleles are protected from malaria; homozygous normal has no protection and homozygous sickle-cell has symptoms such as low tolerance for exertion and a shortened life span. This is an example of

A) stabilizing selection.
B) directional selection.
C) disruptive selection.
D) balancing selection.
E) cryptic selection.