Scientists find dense rock on earth's surface that is made of magnesium and smaller amounts of silicon. what layer of earth might the rock scientists study?

What are the types of genetic recombination

Look at the picture below . what does this picture represent ?

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.