What is an example of a good effect from mutation?

One example of a beneficial mutation is the sickle-cell allele. In its homozygous form, the sickle-cell allele causes sickle cell anemia, a serious disease that leads to chronic pain and organ damage. However, in its heterozygous form, the sickle-cell allele provides protection against malaria, a life-threatening parasitic infection. People who carry one copy of the sickle-cell allele and one copy of the normal allele are less likely to develop malaria than people who have two copies of the normal allele. This is because the sickle-shaped red blood cells that are produced by the sickle-cell allele are more resistant to infection by the malaria parasite. The sickle-cell allele is thought to have originated in West Africa, where malaria is common. It is now found in people of African descent all over the world.