Which of the following amino acid substitution is responsible for causing sickle cell
anemia?
A. Valine is substituted by Glutamic acid in the α globin chain at the sixth position
B. Valine is substituted by Glutamic acid in the β globin chain at seventh position
C. Glutamic acid is substituted by Valine in the α globin chain at the sixth position
D. Glutamic acid is substituted by Valine in the β globin chain at the sixth position