Final answer:
The sickle cell gene persists because heterozygous individuals with one copy of the gene exhibit a trait that provides resistance to malaria, a survival advantage in malaria-endemic regions. This selective advantage keeps the gene prevalent in populations where malaria is common, despite the health complications associated with its homozygous state.
Step-by-step explanation:
Understanding How Natural Selection Favored the Sickle Cell Trait
Sickle cell anemia is a genetic condition wherein red blood cells assume a sickle or crescent shape due to a mutation in the hemoglobin gene. This abnormal shape can cause blockages in capillaries, leading to a plethora of health issues including severe pain and organ damage. The condition is most prevalent among individuals of African descent.
Despite the severe health ramifications of sickle cell anemia, the sickle cell gene persists at a relatively high frequency in regions where malaria is endemic. This biological peculiarity intrigued the British biochemist J.B.S. Haldane, who initially connected high incidences of hemoglobin disorders with malaria-prone regions in the 1940s. Individuals with one sickle cell allele, known as heterozygotes, exhibit sickle cell trait and are generally asymptomatic yet retain some resistance to malaria, caused by the parasite Plasmodium falciparum.
The connection lies in the means by which the malaria parasite reproduces within the red blood cells. In individuals with the sickle cell trait, the presence of abnormal hemoglobin hinders the parasite's lifecycle, providing a survival advantage against the disease. As such, individuals heterozygous for the sickle cell mutation are better adapted to survive in areas where malaria is prevalent. Therefore, through the process of natural selection, the sickle cell allele has been maintained in the gene pool in malarial regions because it confers a protective effect, illustrating a classic example of a balanced polymorphism where the allele is detrimental in homozygotes but advantageous in heterozygotes.