FIGURE 3 A comparison of (a) a normal, uniform, cup-shaped erythrocyte with (b) a sickle-shaped erythrocyte seen in sickle-cell anemia. (c) The shape change in the hemoglobin molecule, due to the substitution of a Val for a Glu residue in the β chain, allows the molecules to aggregate into insoluble fibers within the erythrocytes.