Explanation

11th. Thalassaemia (i) It is an autosome-linked recessive disesase (ii) It occurs due to either mutation or deletion resulting in reduced rate of synthesis of one of globin chains of haemoglobin (iii) Anaemia is the characteristic of this disease (iv) Thalassaemia is classified into two types $\mathbf{\alpha}$-thalassaemia Production of $\alpha$-globin chain is affected. It is controlled by the closely linked genes HBA1 and HBA2 on chromosome 16. It occurs due to mutation or deletion of one or more of the four genes. $\mathbf{\beta}$-thalassaemia Production of $\beta$-globin chain is affected. It occurs due to mutation of one or both HBB genes on chromosome 11