Why is the sickle cell allele prevalent in people of African descent?

• A. It is a result of genetic drift in small populations.
• B. It enhances oxygen transport in red blood cells.
• C. It increases resistance to all infectious diseases.
• D. It provides a survival advantage against malaria.

Answer: (D)

Verified step by step guidance

1. Understand the concept of sickle cell allele: The sickle cell allele is a variant of the hemoglobin gene that can cause red blood cells to become misshapen, or 'sickle-shaped', under low oxygen conditions.
2. Recognize the relationship between sickle cell allele and malaria: Individuals who carry one copy of the sickle cell allele (heterozygous) have a survival advantage in regions where malaria is prevalent because the altered shape of red blood cells can inhibit the malaria parasite's lifecycle.
3. Explore the geographical prevalence: Malaria is common in certain regions of Africa, which explains why the sickle cell allele is prevalent among people of African descent. The allele provides a selective advantage in these areas.
4. Consider the concept of natural selection: The sickle cell allele is maintained in the population due to natural selection, where individuals with the allele have a higher chance of survival and reproduction in malaria-endemic regions.
5. Clarify why other options are incorrect: The sickle cell allele does not enhance oxygen transport, nor does it increase resistance to all infectious diseases. Genetic drift is less likely to explain its prevalence compared to the selective pressure exerted by malaria.