The two closely linked genes HBA1 and HBA2 are associated with

The correct answer is Option (1) → α thalassemia

Option (1) α thalassemia — Correct. HBA1 and HBA2 are the two linked genes of α thalassemia; NCERT places them on chromosome 16 of each parent.

Option (2) β thalassemia — Incorrect. β thalassemia is controlled by the single gene HBB on chromosome 11.

Option (3) Haemophilia — Incorrect. Haemophilia is a sex-linked recessive disorder of a blood-clotting protein. Its gene lies on the X chromosome, not among the HBA genes.

Option (4) Sickle cell anaemia — Incorrect. Sickle-cell anaemia is a change in the β-globin gene.

NCERT Extract:
Mendelian Disorders – “… In α Thalassemia, production of α globin chain is affected while in β Thalassemia, production of β globin chain is affected. α 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 alpha globin molecules produced.”