Sickle cell anemia is caused by mutations in the HBB gene located on chromosome 11p15.4, which provides instructions for making beta globin. A point mutation in this gene produces hemoglobin S, which replaces normal beta globin and causes red blood cells to take on a sickle shape. The disease follows an autosomal recessive pattern of inheritance, where individuals must inherit two copies of the mutated gene - one from each parent who carries the sickle cell trait - in order to have sickle cell anemia.