Please tell me the cause of sickle cell anemia?

Stiffened hemoglobin: There is a genetic change that causes an abnormal hemoglobin. This abnormal hemoglobin becomes stiff in certain circumstances, causing the red blood cell to sickle. This causes many symptoms, including anemia, pain, and many other symptoms.

Gene defect: Years ago a mutation in a gene (set of instructions) used to form hemoglobin appeared. A single gene of a pair conferred some resistance to malaria, a germ that invades red cells. With a normal gene paired with the defect, they were able to live normally. If 2 defective genes appear in a person, their red cells are stiff & breakdown quickly (anemia) & are unable to get easily through capillaries.