This post was originally published on December 16, 2007.
Not half bad? How can a disease be â€śnot half badâ€ť? Well, in a way, sickle cell anemia isnâ€™t â€śhalf badâ€ť at all! Sickle cell anemia is a disorder of the red blood cells that mainly occurs in African countries. Itâ€™s a genetic disorder where a personâ€™s red blood cells are misshapen and do not efficiently carry oxygen throughout the body. It is a recessive condition which means a person must inherit only the recessive alleles (or genes) that code for their red blood cells to have this deformity.
The hemoglobin on the red blood cells does not properly deliver oxygen to other parts of the body, so someone who has this disorder will have multiple health problems and a much shorter lifespan. Someone who has hybrid (both dominant and recessive) alleles has red blood cells with mixed (or half!) sickle cells along with normal cells and will exhibit only minor health problems.
So how is sickle cell anemia only half bad? Well, a very deadly epidemic known as malaria has been sweeping Africa for thousands of years. It is caused by a parasite and it works by infecting the blood cells of its host. But, the amazing thing is that it cannot infect sickle cells. So if you have sickle cells you canâ€™t get malaria! But, what does it matter if they canâ€™t get malaria when theyâ€™re lifespan might only be a little bit longer with anemia?
The phenomenon lies in the hybrids (people with both the dominant and recessive alleles). Since they have sickle cells, malaria cannot infect them! Even better, since they also have normal blood cells, they are generally fairly healthy.
This phenomenon is referred to as heterozygote advantage (the hybrid allele combinations are called heterozygous), meaning that the heterozygous individual is more apt to survive than individuals with either the only dominant or only recessive allele combinations.
Confused? Thereâ€™s a whole lot of confusing vocabulary in this post. If you are, just check the source. It really accurately defines everything and helps you to understand the specifics.
Can you find any other diseases or disorders that have this heterozygote advantage?Â Do you have any unanswered questions about this concept or any comments about the condition itself?