As Many as 60% of People in Malaria-Infected Regions of Africa

question 20

Multiple Choice

As many as 60% of people in malaria-infected regions of Africa have the sickle-cell allele, but only about 10% of the U.S. population of African ancestry carries the allele. Malaria remains a major disease in central Africa but has not been a serious problem in the U.S. for many generations. What is/are the reason(s) for the difference in the percentages and what is a reasonable statement about future percentages?

• A) The presence of malaria in Africa maintains the advantage of the heterozygous sickle-cell trait, and the prevalence of malaria will likely continue to preserve the 60% rate.
• B) The U. S. percentage may have always been somewhat lower due to immigration from nonmalaria regions, but changes in sites and rates of immigration could occur.
• C) Lack of widespread malaria in the United States would have made both homozygous and heterozygous carriers of sickle-cell undergo several generations of negative selection, and we should expect this to continue unless innovative therapies give all individuals an equal chance of surviving and reproducing.
• D) All of the choices are reasonable.

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Definitions:

Electrical Resistance

A measure of the degree to which an object opposes the passage of an electric current.

Ventricular Contraction

This refers to the phase in the cardiac cycle where the ventricles (lower chambers of the heart) contract to pump blood out to the body and lungs.

Apex

Extremity of a conical or pyramidal structure. The apex of the heart is the rounded tip directed anteriorly and slightly inferiorly.

AV Bundle

The bundle of His, which is a collection of heart muscle cells specialized for electrical conductivity that transmits the electrical impulses from the AV node to the point of the apex of the fascicular branches.