"Sickle cell anemia is an inherited condition which results in some erythrocytes being malformed. The gene for this condition causes the hemoglobin to be incorrectly formed, which in turn causes some erythrocytes to take on a crescent shape. These cells are not able to carry adequate amounts of oxygen to cells."
(
http://www.unomaha.edu/hpa/blood.html)
You should probably talk about hemophilia and such...