Final answer:
Sickle cell anemia is caused by a mutation in the hemoglobin gene, leading to sickle-shaped red blood cells. Being heterozygous for this trait offers protection against malaria, providing a selective advantage in certain regions. This natural selection effect maintains the allele within populations in malaria-endemic areas.
Step-by-step explanation:
Sickle Cell Anemia and Its Role in Natural Selection
Sickle cell anemia is a genetic condition that results in red blood cells assuming a crescent or sickle shape. This condition is caused by a mutation in the hemoglobin gene. Hemoglobin is a protein in red blood cells that carries oxygen throughout the body. The mutation leading to sickle cell anemia causes a single base change in the gene for human b-hemoglobin. People who are homozygous for the sickle cell allele (SS) suffer from sickle cell anemia, while heterozygous individuals (AS) carry the sickle cell trait but generally do not exhibit symptoms of the disease.
In areas where malaria is prevalent, the sickle cell allele provides a survival advantage. Heterozygotes (AS) show resistance to malaria, a significant benefit as it increases their chances of survival and reproduction, thus maintaining the allele within the population. This example of natural selection demonstrates how a harmful allele can persist in a population's gene pool due to the environmental advantage it provides in specific contexts.
If malaria were to be eradicated, the survival advantage for heterozygotes would disappear, likely reducing the prevalence of the sickle cell allele. However, due to the historical prevalence of malaria, factors such as the mutation rate and genetic drift could still influence its presence in the gene pool.