Why is sickle cell anaemia a qualitative problem while thalassemia is a quantitative problem?

Dear student,
Sickle-cell anaemia is a disease in which red blood cells become distorted or sickle-shaped. It is a genetic disorder of red blood cells. It does not affect the quantity of red blood cells but affect the quality.
Thalassaemia is an inherited blood disorder in which the production of alpha nad beta globin chains are effected which inhibits the production of haemoglobin. Thus the number of red blood cells are lowered.
Thus sickle cell anaemia is qualitative disorder whereas thalassemia is a quantitative disorder of red blood cells.
Regards