Sickle shaped cells arise from abnormal:

1. The defect lies in the oxygen carrying protein. 2. The altered protein distorts the cell. 3. Erythrocytes produce an abnormal type of hemoglobin, which causes the sickle or crescent shape. 4. So the answer is hemoglobin. _Source: OpenStax 'Anatomy and Physiology 2e', Ch 18 'Blood'_