Final answer:
Sickle cell anemia is a balanced polymorphism with a heterozygous advantage because carriers are protected from malaria infection, while homozygous individuals have a potentially lethal blood disorder. The presence of the sickle cell gene provides protection against malaria in regions where the disease is prevalent.
Step-by-step explanation:
Sickle cell anemia is a good example of a balanced polymorphism with a heterozygous advantage because heterozygous carriers are protected from malaria infection, while individuals who are homozygous for the sickle cell mutation have a potentially lethal blood disorder. This heterozygous advantage occurs in regions where malaria is prevalent, as the presence of the sickle cell gene provides protection against the disease. In this balanced polymorphism, the frequency of the S allele remains stable in the gene pool due to the selective advantage of being a carrier.