DNA amplification is done without purification of the cellular DNA with PCR. Of all genetic diseases, the inherited haemoglobin disorder has been the most extensively studied at the DNA level. In what follows, Haemoglobinnopathies will be taken as examples. Their antenatal diognosis by recombinant DNA techniques has served as a prototype for other genetic disorders. Clinically the most important Haemoglobinnopathies are sickle cell anaemia and the thalassaemia site in genomic DNA.

This can be used as all Marker for the presence or absence of the defect. Digesting the mutated and normal DNA with the restriction enzyme and performing Southern-blot hybridization with a cloned β-globulin DNA probe can therefore detect the mutation.

Such an approach is applicable only to those disorders where there is an alteration in a restriction site or where a major deletion or rearrangement alters the restriction pattern.