Individuals Who Carry Two Copies of the Allele for the Sickle-Cell

Short Answer

Individuals who carry two copies of the allele for the sickle-cell form of hemoglobin suffer from a usually fatal anemia. However, individuals who carry one sickle-cell allele have a greater resistance to malaria. Such individuals demonstrate the principle of _______, which accounts for the maintenance of both the normal and the sickle cell alleles.