The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-saharan africa than among those of african descent living in the united states. even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-saharan africa but absent in the united states. discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions.

Ans.

Sickle-cell disorder is a genetic disorder, which shows defected red blood cells, due to mutation in the genes for hemoglobin protein.

Malaria is common in sub-Saharan Africa region and there, natural selection favored gene for sickle cells, because it might be beneficial to people having sickle cell disease that makes them able to survive in such condition and transmit their genes to offspring.

On the other hand, in those Africans, who moved to United States, where malaria is uncommon or absent, natural selection favored normal, wild type genes, resulting in fewer people with defected sickle cell.

Hence,  sub-Saharan African population shows higher percentage of mutated gene for sickle cell as compared to population of United States.

Thus, the evolutionary process behind this difference is 'natural selection.'