DNA sequence changes within a gene result either in polymorphism or mutation, causing different diseases. Some of these polymorphisms that occur with a high frequency within the population can be a useful tool for gene tracking for a given disease. Such investigations have initially been done by Southern blot techniques, but, where possible, they have now been replaced by polymerase chain reaction (PCR)-based methodology. The nucleotide substitutions can be identified in two ways:

1.	By use of restriction enzyme analysis or restriction fragment length polymorphisms (RFLPs).
2.	Allele specific oligonucleotide hybridization (ASO-H) or similar techniques.