$\mathrm{\alpha }$-thalassemia is controlled by ___(i)___ gene present on ___(ii)___ chromosome.

	(i)	(ii)
1.	HBA1 and HBA2	16
2.	HBB	11
3.	HBB	16
4.	HBB and HBA2	11

$\mathrm{\alpha }$ thalassemia is controlled by two closely linked genes HBA1 and HBA2 on chromosome 16 of each parent and it is observed due to mutation or deletion of one or more of the four genes. The more genes affected, the less $\mathrm{\alpha }$ globin molecules produced. $\mathrm{\beta }$ Thalassemia is controlled by a single gene HBB on chromosome 11 of each parent and occurs due to mutation of one or both the genes.