Final answer:
Sickle cell disease is caused by production of abnormal hemoglobin, which delivers less oxygen to tissues and causes the red blood cells to assume a sickle shape. This can lead to problems such as blocked blood flow and serious health complications.
Step-by-step explanation:
A characteristic change in the shape of erythrocytes is seen in sickle cell disease (also referred to as sickle cell anemia). A genetic disorder, it is caused by production of an abnormal type of hemoglobin, called hemoglobin S, which delivers less oxygen to tissues and causes erythrocytes to assume a sickle (or crescent) shape, especially at low oxygen concentrations. These abnormally shaped cells can then become lodged in narrow capillaries because they are unable to fold in on themselves to squeeze through, blocking blood flow to tissues and causing a variety of serious problems from painful joints to delayed growth and even blindness and cerebrovascular accidents (strokes).