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Sickle Cell Anemia is an example of balanced polymorphism. Balanced polymorphism is when a trait is selected, and maintained, in a population, because there is a specific advantage through the heterozygous condition. Sickle Cell Anemia originated through a mutation, which is of course one of the forces of evolution. When a person is heterozygous for the trait, they are resistant to Malaria, however, when they are homozygous, they have sickle cell anemia

Now, if you are not a biology major, this probably isn’t making much sense, so let’s back up. There are two alleles in this trait, “A” is normal hemoglobin, “S” is the one for Sickle Cell Anemia. If someone has two “A” alleles, they are totally normal, however they can get malaria. If someone has two “S” alleles, they are typically anemic, due to the irregular shape of their hemoglobin. However, if someone has one “S” allele, and one “A” allele, they are resistant to malaria, and their cells are shaped normally.

There’s only one big problem with being heterozygous for the trait. If two heterozygous people have kids, one out of four of their kids will be homozygous for the trait, therefor, they will be anemic. Two out of four of their kids will be heterozygous, therefor, resistant to malaria, and one out of four of their kids will have normal hemoglobin.

How did this trait become prevalent? In certain parts of Africa, malaria crept into existence. Many people died from this disease (spread through mosquitoes), however, there were a few people in the population that had a mutation that made them resistant to malaria. This trait was then naturally selected into existence.

Today, malaria is primarily present in Africa, Asia and Latin America. Fortunately the disease can be treated by “antimalalial” drugs. However the parasites have slowly developed a resistance against some of the drugs. Many people cannot afford the medicine that treats malaria. The cure costs the equivalent of ten days work for the average person in a third world countries. Over one million people die each year of the disease.

Although our society has advanced to a point where we can treat and cure malaria, the sickle cell trait is still useful in areas of the world medicine is not readily available. People homozygous for Sickle Cell Anemia can also be treated when care is available. Regular blood transfusions and an array of medication allow for a longer life and better health.

Malaria is currently present in locations which are home to more than 40% of the world’s population. Although many people look at Sickle Cell Anemia is an intolerable burden, in reality it saves many lives.