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Solution:

DNA fingerprinting is a method for comparing the DNA sequences of any two individuals.

The sample like blood, hair follicles etc are collected at the site of crime and then the DNA is separated from them. The DNA is matched with the suspected persons to identify the criminals. The complete procedure is given below:

  • VNTR (variable number of tandem repeats) are satellite DNAs that show high degree of polymorphism.
  • VNTRs are used as probes in DNA fingerprinting. The VNTR are highly variable in different individuals.
  • First of all, DNA from an suspected person is isolated and cut with restriction 
  • endonucleases.
  • Fragments are separated according to their size and molecular weight on gel electrophoresis.
  • Fragments separated on electrophoresis gel are blotted (immobilised) on a synthetic membrane such as nylon or nitrocellulose.
  • Immobilised fragments are hybridised with a VNTR probe.
  • Hybridised DNA fragments can be detected by autoradiography.
  • VNTRs vary in size from 0.1 to 20 kb.
  • Hence, in the autoradiogram, band of different sizes will be obtained.
  • These bands are characteristic for an individual. They are different in each individual except identical twins.
  • They are then matched with the DNA obtained from the samples at criminal site. 

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