Why is thalassaemia categorised as a Mendelian disorder ? Write the symptoms and explain the cause of the disease. How does it differ from sickle cell anaemia ?

Explanation

Symptoms. (i) There is reduced synthesis of either `alpha` or ` beta `chains of haemoglobin (less number of chains due to precipitation). (ii) The reduced synthesis of a-chains leads to damage to the precursion of RBCs in the bone marrow causing severe haemolytic anaemia (Hb level lower than normal). (iii) The lifespan of RBCs is short 30-40 days, even though the number of RBCs is absolutely normal. (iv) Globin variation can inhibit the binding of oxygen in hence and distorts the shape of entire RBC. Cause. It is an autosome linked recessive disease, is transmitted, when both the partners are unaffected carriers. The defect could be due to either substitution or deletion of N-bases. In a thalassaemia out of four genes, two linked genes (HBA1, HBA2) from each parent on chromosome 16, one or more of these may mutate (variant) or become missing. People with one gene affected are called .silent carriers. and have no sign of illness, with 2 depective alliles produce a-thalassaemia minor. The babies with all the four genes affected could not survive and usually died before birth. In `beta` thalassaemia, also called Cooley.s anaemia, two genes (HBB), on chromosome 11 one from each parent, are involved and disease may be due to one or both of the two genes variant. (with one defective allile suffer from the thalassemia minor and with both defective allieles suffer from colley.s anaemia or thalassemia major.) There is accumulation of a chains due to decreased synthesis of `beta `-chains, Thalassaemia differs from sickle cell anaemia in being a quantitative problem of synthesising too few globin molecuies while sickle cell anaemia is qualitative problem of synthesising an incorrectly functioning globin.