An online article that your professor asked you to critique states that African Americans cannot contract malaria, even if they go to endemic areas, because of a genetic trait that confers protection from the disease. Why is this article incorrect

Balanced polymorphism implies that not the entire population of African Americans are heterozygous for the sickle cell trait.

It is worthy to note that immunity from malaria isn't derived or given to an individual by genes. African Americans do have an higher tendency to show thalassemia, which can't offer immunity to an individual totally from the symptoms malaria.

This case study is an example of Natural selection in humans and unusual hemoglobins and immunity to malaria. The heterozygous persons for the sickle cell gene stands at an higher probability of overpowering or not showing the symptoms of malaria than both classes of homozygous persons.

This implies that for either alleles-the sickling allele and the normal allele-are kept at a relatively constant frequency, implying to the heterozygote possessing a kind of balanced polymorphism. As the homozygous individuals do not show immunity against malaria, it is not justifiable and inadequate to establish a blanket statement that all African Americans are protected from malaria.