Malaria and the Sickle Cell Gene

      One of the most fascinating things I have ever learnt about malaria is the relationship between malaria and  the sickle cell gene. First I will give a little background about the sickle cell gene. Normal red blood cells that carry oxygen around the body are shaped like biconcave discs.
        In people with sickle cell anemia, the red blood cells have a sickle or crescent shape, hence they are unable to effectively carry oxygen around the body like they should. Those who are homozygous for this gene have the genotype HbSS and they are said to have sickle cell anemia. Those who are heterozygous for this gene have the genotype HbAS and they are said to have the sickle cell trait. These people do not experience any of the complications of sickle cell anemia.   This change in shape of RBCs is caused by  an abnormal type of hemoglobin called hemoglobin S. People who are heterozygous for the sickle cell gene meaning the have one allele for the normal hemoglobin and one allele of the sickle hemoglobin have been found to have increased immunity against malaria.
       It has been found that there is a high frequency of the sickle cell gene in places where malaria is endemic despite the many deaths from complications of sickle cell anemia among homozygotes in these areas.This is an example of natural selection. The high frequency of this gene has been found to be due to the selective advantage conferrred by HbAS against malaria mortality. In other words, even though people who are homozygous for this gene experience multiple complications and deaths, nature still keeps this gene at a high frequency in those areas to which malaria is endemic because of the protection that the gene offers agianst malaria.

References

1. Khairy, K., Foo, J. J., & Howard, J. (2010). Shapes of red blood cells: Comparison of 3d confocal images with the bilayer-couple model. Cell Mol Bioengineering , 1(2-3), 173-181. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2963995/

2. Thomas, N. W., Mwangi, T. W., & Roberts, D. J.  et al (2005). An immune basis for malaria protection by the sickle cell trait. PLOS Medicine, 2(5), 0041-0045. Retrieved from http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0020128