Final answer:
Sickle-cell anemia is most prevalent among African Americans due to the sickle-cell gene offering resistance against malaria. This trait has persisted especially in regions where malaria is endemic, despite the health problems associated with having two copies of the gene. The correct option is 1.
Step-by-step explanation:
Sickle-cell anemia is most common among African Americans. This blood disease is characterized by an abnormally shaped hemoglobin protein which causes red blood cells to take on a sickle or crescent shape. Individuals with this disease often face complications as the misshapen cells can obstruct narrow blood vessels, leading to tissue damage and other serious health issues.
The allele causing sickle-cell anemia found in individuals of African descent in the Western Hemisphere is believed to have originated from West Africa. Despite the diseased state, the sickle-cell gene offers a selective advantage against malaria, which is why it persists in the population. This protective trait against malaria is notably beneficial for heterozygotes with the sickle cell trait in malaria-endemic regions.
Sickle-cell anemia affects a significant number of people worldwide, including 8-10% of African Americans. In regions where malaria is prevalent, such as Africa, individuals with one sickle cell allele (carriers of the trait) are more likely to survive and reproduce, leading to the continued presence of the sickle-cell gene. Therefore, this demonstrates a classic case where a detrimental genetic condition is maintained in a population due to its advantage in certain environmental contexts.