→ As polymorphism in DNA sequence is the basis of genetic mapping of human genome as well as of DNA fingerprinting, it is essential that we understand what DNA polymorphism means in simple terms.
→ Polymorphism (variation at genetic level) arised due to mutations.
→ New mutations may arise in an individual either in somatic cells or in the germ cells (cells that generate gametes in sexually reproducing organisms).
→ If a germ cell mutation does not seriously impair individual's ability to have offspring who can transmit the mutation, it can spread to the other members of population (through sexual reproduction).
→ 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.
→ The probability of such variation to be observed in non-coding DNA sequence would be higher as mutations in these sequences may not have any immediate effect/ impact in an individual's reproductive ability.
→ These mutations keep on accumulating generation after generation, and form one of the basis of variability / polymorphism.
→ There is a variety of different types of polymorphisms ranging from single nucleotide change to very large scale changes.