Which of the following is incorrect about HBB gene of human?

$\mathrm{\alpha }$ thalassemia is controlled by two closely linked genes HBA1 and HBA2 on chromosome 16.

$\mathrm{\beta }$ thalassemia is one of the most common recessive genetic diseases, caused by mutations in the HBB gene found on chromosome 11. Over 200 different types of mutations in the HBB gene containing three exons have been identified in patients with β-thalassemia whereas a homozygous mutation in exon 1 causes sickle cell anemia (SCA). Thus, SCA is caused due to point mutation (change of a single base pair in DNA) in the gene coding for $\mathrm{\beta }$-chain of hemoglobin. Thalassemia is a quantitative problem of too few globins synthesised, whereas sickle-cell anemia is a qualitative problem of synthesis of an incorrectly functioning globin.