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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.

Rarefaction is used for which of the following? a. creating a representative sample b. studying how disease impacts populations c. rediscovering species thought to be instinct d. determining which sea creatures live in an area

Some steps in cell division are shown below: 1. chromosomes condense and pair up 2. segments of dna of sister chromatids twist and cross 3. exchange of dna occurs between chromosomes 4. four daughter cells are created that are haploid which of the following steps is least likely to occur during meiosis 1?