Which of the following explains why sickle-cell disease continues to persist in Africa?

• A. Sickle-cell disease is a new mutation that has recently appeared in Africa.
• B. Sickle-cell disease is caused by a virus that is prevalent in Africa.
• C. Sickle-cell disease is a result of poor healthcare systems in Africa.
• D. Sickle-cell disease provides a survival advantage against malaria.

Answer: (D)

Verified step by step guidance

1. Understand the genetic basis of sickle-cell disease: It is caused by a mutation in the hemoglobin gene, leading to the production of abnormal hemoglobin known as hemoglobin S.
2. Recognize the relationship between sickle-cell disease and malaria: Individuals who are heterozygous for the sickle-cell trait (carrying one normal hemoglobin gene and one sickle-cell gene) have a survival advantage in regions where malaria is prevalent.
3. Explain the mechanism of this advantage: The presence of hemoglobin S in red blood cells can interfere with the lifecycle of the malaria parasite, reducing the severity of the infection.
4. Consider the evolutionary perspective: In areas where malaria is common, the sickle-cell trait is naturally selected because it increases the likelihood of survival and reproduction, thus maintaining the presence of the trait in the population.
5. Conclude with the persistence of sickle-cell disease: Despite its health challenges, the sickle-cell trait continues to be prevalent in Africa due to its protective effect against malaria, illustrating a case of balanced polymorphism.