What does reproductive isolation within a species cause

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.

The breakdown of food is accomplished by enzymes. a. physical b. chemical c. mechanical d. none of the above

What determines whether a particular cell is able to respond to a hormone?