a) Explain DNA polymorphism as the basis of genetic mapping of human genome.
b) State the role of VNTR in DNA fingerprinting.

Explanation

(a) If an inheritable mutation is observed in a population at high frequency. it is referred to as DNA polymorphism. The probability of such variations to be observed in non coding DNA sequence would be higher as mutations in these sequences may not have any immediate effect in an individual's reproductive ability. These mutations keep on accumulating generation after generation and form one of the basis of variability/polymorphism ranging from single nucleotide change to very large scale changes. Such DNA segments are called repetitive DNA and show high degree polymorphism and form the basis of DNA fingerprinting
(b) VNTR (Variable Number of Tandem Repeats) belongs to a class of satellite DNA referred to as mini-satellite. A small DNA sequence is arranged tandemly in many copy numbers. The copy numbers vary from chromosome to chromosome in an individual. The numbers of repeat show very high degree of polymorphism. As a result the size of VNTR varies in size from 0.1 to 20 kb. Consequently, after hybridisation with VNTR probe, the autoradiogram gives many bands of different sizes. These bands give a characteristic pattern for an individual DNA. It differs from individual to individual in a population except in the case of identical twins.