In the United States, the parasite that causes malaria is not present, but African-Americans whose ancestors were from equatorial Africa are present. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?

Directional selection; stabilizing selection

Explanation:

The stabilizing selection is a result of the decrease of the population and causes genetic variation due to the natural selection.  The directional selection of the genetic variation shifts to a new phenotype and on exposure to the environmental changes and both of these can lead to the natural selection and contribute to the variation of the population.