A close-up view. The polymerized hemoglobin distorts red blood cells into an abnormal sickle shape. A stops polymerization, preventing serious sickling. The pure hemoglobin S in homozygotes polymerizes to a greater degree.
Red cells lyse in homozygotes, producing the disease 'sickle cell anemia'.
Sickle hemoglobin, even in heterozygotes, confers resistance to one type of malaria.