What is $DNA$ polymorphism ? Why is it important to study it ?

Polymorphism (variation at genetic level) arises due to mutations. Allelic sequence variation has traditionally been described as a $DNA$ polymorphism if more than one variant (allele) at a locus occurs in human population with a frequency greater than $0.01$. In simple terms, if an inheritable mutation is observed in a population at high frequency, it is referred to as $DNA$ polymorphism.

Polymorphism become very useful identification tool in forensic applications. Further, as the polymorphisms are inheritable from parents to children, $DNA$ fingerprinting is the basis of paternity testing, in case of disputes.