For some conditions, having one mutated copy of a gene in each cell is advantageous,
while having two mutated copies causes disease. The best-studied example of this
phenomenon is sickle cell disease: Having two mutated copies of the HBB gene in each
cell results in the disease, but having only one copy provides some resistance to
malaria. This disease resistance helps explain why the mutations that cause sickle cell
disease are still found in many populations, especially in areas where malaria is
prevalent.
What mechanism of evolution is this?
Founders effect
Mutations
Geographic Isolation
coevolution