Sickle-cell anemia is a disease that occurs when a person is homozygous for a particular allele, s, and this condition is very often fatal.

Sickle-cell anemia is a disease that occurs when a person is homozygous for a particular allele, s, and this condition is very often fatal. It might seem odd that there would be an allele that causes a fatal disease. You probably wonder why selection hasn't gotten rid of this allele and we're going to help you figure that out.