How many of the given statements are incorrect?
I. Thalassemia is caused due to mutation in only chromosome 21
II. Mutation on either chromosome 11 or 16 may cause sickle cell anaemia
III. At the 6th position beta globin chain, glycine is replaced by glutamic acid in case of sickle cell anaemia
IV. Phenylketonuria is caused due to lack of enzyme phenylalanine tyrosinase