$\beta$-thalassaemia. major is also known as Cooley's Anemia

Thalassaemia have two major kinds

$\alpha$-thalassaemia and $\beta$-thalassaemia.

According to defective gene in $\alpha$ or $\beta$-chain of haemoglobin.

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

$1.$ $\alpha$-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.

$2.$ $\beta$-thalassaemia Production of $\beta$-globin chain is affected. It occurs due to mutation of one or both HBB genes on chromosome $11$