Final answer:
The proportion of individuals with sickle cell anemia differs globally and is about 8-10% among African Americans. Heterozygotes for the sickle cell trait have a defensive advantage against malaria, which is believed to contribute to the prevalence of the gene in certain areas despite its associated health risks. Homozygous individuals with sickle cell anemia have severe health issues but derive minimal benefit from the anti-malarial effect.
Step-by-step explanation:
The proportion of individuals in a population who have sickle cell anemia can vary widely depending on geographic location and ethnic background. For example, sickle cell gene affects perhaps more than 100 million people worldwide, and in the United States, the prevalence among African Americans is between 8-10%. In some parts of Africa, the sickle cell trait, which is heterozygous (meaning one sickle cell allele and one normal allele), provides a protective advantage against malaria. Haldane's hypothesis suggests that this advantage explains why the sickle cell gene remains relatively common despite the survival challenges associated with sickle cell anemia.
Sickle cell anemia is caused by a genetic mutation in the beta-hemoglobin gene, leading to red blood cells that have a crescent or sickle shape. These misshaped cells can cause serious health issues, and individuals with two copies of the sickle cell gene (homozygotes) are most severely affected. While the trait can confer resistance to malaria in heterozygous individuals, homozygous individuals derive little benefit from its anti-malarial effects. Despite this, the sickle cell gene persists in the population, especially among descendants of people from areas where malaria is or was endemic.