Biology Help?

Question

In the United States, 8 percent of African Americans are carriers for the sickle-cell allele, while in central Africa the figure is 20 percent. What could account for this difference? Assess.

Answer 1

Because in America, we consider any black person African American. Yet many are not from Africa. Some individuals are from the West Indies for example. On the other hand, black people in Africa are, by the very definition, African. It would seem to me that the Sickle Cell allele mutation originated in the continent of Africa and those individuals from other regions of the world are not prone to have or pass on the allele.

Answer 2

There's some truth to all the above answers. However, I suspect that your test question refers more to evolutionary change than to population mixing and genetic 'dilution'. Think about this: In central African regions where the sickle-cell trait developed, it plays a protective role against malaria, which is quite a deadly disease. In the US, where malaria was eradicated as common health problem many years ago, the people who don't have the sikle-cell trait are not 'weeded out', while the people who do have the sickle-cell trait run into severe to life-threatening health problems. Now the selective pressure operates only against the people who have the trait, instead of more strongly against the people who _don't_ have it. Since having the trait makes you less likely to have kids (and some of those kids won't have kids), the trait is gradually vanishing from the US population. Meanwhile in areas where malaria is still a serious health problem, having the trait is still less risky than not having it. You still have the same health problems as the folks in the US who have it, but you're at less risk of serious problems from malaria. Now this can change; if malaria becomes less of a public health risk in Africa, then the relative number of sickle-cell carriers should start to go down. Meanwhile, as malaria becomes more of a public health problem in the US, you would expect the relative sickle-cell numbers to stop dropping and maybe start going up.

Answer 3

Sickle cell is more prevalent in Africa because fewer medicines for malaria are available. People with sickle cell rarely contract malaria and therefore aren't afflicted with the disease. In the US malaria is very rare and survival of the fittest tells us that the genetic variation is no longer necessary.

Of course our mating behaviors also change the genome, but I believe the question is more one of natural selection than one of straight mating.

Answer 4

The reason it is a smaller percentage in the US than in Africa is because of more, and longer time span, of cross breeding with other nationalities.

Answer 5

not all africans come from central africa, many may have come before it spread into that region and so the #'s are less

Answer 6

Genes...persons are constantly evolving, americans may have evolved differently over time based on surroundings.