Malaria and Sickle cell anemia In USA we do not have Mataria because the protist

Question

Malaria and Sickle cell anemia In USA we do not have Mataria because the protist causing the disease (Plasmodium is not.present However, there are people that carry the atele that causes sckle cell anemia, in the heterozygous condition (AS) Most of these people do not suffer greatly from the disease,they are simply neterozyous for the conditon. One would expect that the allele for sickle anemia (s) would disappear from the popuiation.inUSA since here is no heterozygote advantage and homozygous for S dlie earty in life. However this is untikely to happen. Why I can think of at least two reasons but more are likety. You get fult credit if you can successtulty articulate one reason

Explanation / Answer

In areas where frequent malaria outbreaks takes place, individuals with the heterozygous state have a distinct advantage. These individuals who are carriers for sickle trait possess a resistance to malarial infection. Plasmodium that causes malaria spends part of its cycle in the red blood cells and triggers an abnormal drop in oxygen levels in the cell. In carriers, when the oxygen level drops, it triggers a full sickle cell reaction, which leads to infected cells being rapidly removed from circulation and controlling the plasmodium infection. Hence, the carriers for SCA have a great resistance to infection and have a greater chance of surviving malarial outbreaks.

Individuals who are homozygous for SCA may survive malaria, but will die from SCA. Individuals with normal alleles will may not have children who are carriers or affected for SCA, but are susceptible to malaria. This resistance to the malarial infection is the primary reason the SCA allele and SCA disease still exist.

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