Sickle-cell anemia is caused when a mutation results in the replacement of glutamate with valine. Witch type of mutation is observed here?

The mutation that causes the sickle-cell disease is a mutated form of hemoglobin called HbS being formed. The S is for the word sickle. The only difference between a normal hemoglobin and HbS is that one glutamate amino acid residue is being replaced with a valine amino acid residue.