Final answer:
Sickle cell anemia is the type of anemia that causes RBCs to become crescent-shaped due to an alteration in the hemoglobin gene, leading to hemoglobin S production and subsequent blood vessel blockages and health complications.
Step-by-step explanation:
The type of anemia that causes red blood cells (RBCs) to change to a crescent shape is known as sickle cell anemia. This condition is a genetic disorder characterized by the production of an abnormal type of hemoglobin, hemoglobin S. At low oxygen concentrations, these abnormal hemoglobin molecules lead to the deformation of normally biconcave, disc-shaped RBCs into a crescent or sickle shape. This deformation increases the risk of blood vessel blockage and can cause various health complications, including painful joints, delayed growth, and potentially severe conditions like blindness and strokes. Sickle cell anemia affects individuals more commonly of African descent and is a result of a mutation in one of the hemoglobin genes.