Practice problem
Genetic Mutations — Overview & Allele Frequency
Sickle cell disease is a disease caused by a single nucleotide replacement mutation that causes a glutamic amino acid to be replaced with a valine amino acid. This causes red blood cells to have a crescent moon "sickle" shape instead of a round one, and the cells produce much more carbon monoxide than normal. Sickle cell disease can cause severe pain, anemia, bacterial infections, and stroke. However, sickle cell disease only happens when a person has two copies of the mutation (one on each chromosome). A person can be a carrier of the sickle cell disease gene. In that case, only some red blood cells are sickle shaped, but the person is healthy.
Malaria is a different disease caused by a parasite that usually lives in mosquitoes. When a mosquito bites a person, the malaria parasite enters the blood and then tries to live in the red blood cells. As the parasite grows and reproduces, it causes damage to the blood cells, resulting in sickness.
Sickle cell disease is obviously a mutation that can cause harm. Presumably, this would lead to the sickle cell trait becoming less and less common over time. However, in places where mosquitoes are common, the sickle cell gene is very common. What is a possible explanation for this?