Sickle Cell Disease

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A) Individual homozygous with normal hemoglobin are susceptible to have death from malaria. Malaria is endemic and people have a significant chance of dying of acute malarial infection in childhood. Whereas, individual homozygous with sickle-hemoglobin provides neither absolute protection nor invulnerability to the disease. Having one gene for hemoglobin A and one gene for hemoglobin S, have a greater chance to survive the acute illness if they have sickle cell trait and do not suffer adverse consequences from the hemoglobin S gene. The genetic selective scenario in which a heterozygote for two alleles of a gene has an advantage over either of the homozygous states called “balanced polymorphism”. A common misstatement is that malaria selects…show more content…
For millions of years, whenever malaria swept through an area of Africa, those with sickle cell trait had a greater chance of survival than those without the trait. Those with sickle cell trait perpetuated the disease. Even today, in some areas of Africa like Uganda, up to 46% of the population may have sickle cell trait, and 2% have full-blown sickle cell anemia. In areas without malaria, sickle cell anemia and sickle cell trait are disadvantageous because of their debilitating side effects. Those with the disease cannot compete against those without the disease, so reproduce less often. Therefore, the S hemoglobin gene is passed on less frequently in these populations, and the incidence of sickle cell anemia and sickle cell trait decreases. For instance, in the United States, where malaria is not a problem, only 8% of the African-American population has sickle cell trait, and 0.25% have full blown sickle cell anemia. Sickle cell anemia and even sickle cell trait are enough of a disadvantage in malaria-free parts of the world that their frequency of incidence
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