Why is thalassaemia categorized as a Mendelian disorder ? Write the symptoms and explain the causes of the disease.

Thalassaemia is categorized as a Mendelian disorder because it is determined by single alleles mutation it involves the genes HBA1 and HBA2, inherited in a Mendelian recessive fashion. 

Symptoms : People with thalassaemia make less haemoglobin and circulating red blood cells than normal human beings, which results in mild or severe anaemia. 

Cause : Both α and β-thalassaemias are often inherited in an autosomal recessive fashion, although this is not always the case. Thalassaemias are a group of disorders caused by defects in the synthesis of globin polypeptide. Absence or reduced synthesis of one of the globin chains results in an excess of the other. In this situation, free globin chains which are insoluble, accumulate inside the red blood cells and form precipitates, which damage the cells, causing cell lysis and resulting in anaemia. There are two main types of thalassaemias in which synthesis of α or β globin is defective. 

In thalassaemia, patients have a deficiency of either α or β globin. But patients with sickle-cell anaemia have a specific mutant form of globin, causing production of abnormal red blood cells. Sickle- cell anaemia is caused by the mutant recessive allele on chromosome 11.