Sickle-cell disease and hemoglobin C disease are both caused by point mutations, resulting in glutamic acid at position 6 in the β-globin being replaced by and , respectively.

The correct answer is "valine; lysine".

Explanation:

The Sickle-cell disease and hemoglobin C disease are two examples of how a single mutation could have harmful consequences. In Sickle-cell disease, glutamic acid at position 6 in the β-globin is replaced by valine, result of  a glutamic acid codon (GAG) being changed into a valine codon (GTG). In hemoglobin C disease, the same glutamic acid is replaced by lysine, which results in the conversion of the normal hemoglobin A (Hb A) into the structural variant of Hemoglobin C (Hb C).