Monday, July 27, 2020

Molecular Basis of Inheritance - Notes | Class 12 | Part 10: DNA Fingerprinting

6. MOLECULAR BASIS OF INHERITANCE

DNA FINGERPRINTING (DNA PROFILING)

  • It is the technique to identify the similarities and differences of the DNA fragments of 2 individuals.
  • It is developed by Alec Jeffreys (1985).
Basis of DNA fingerprinting
  • DNA carries some non-coding repetitive sequences.
  • Repetitive DNA can be separated from bulk genomic DNA as different peaks during density gradient centrifugation.
  • The bulk DNA forms a major peak and the small peaks are called satellite DNA.
  • Satellite DNA is classified as micro-satellites, mini-satellites etc. based on base composition (A:T rich or G:C rich), length of segment and number of repetitive units.
  • A DNA sequence which is tandemly repeated in many copy numbers is called variable number tandem repeats (VNTR). It belongs to mini-satellite DNA.
  • In a person, copy number varies in each chromosome.
  • The two alleles (paternal and maternal) of a chromosome also contain different copy numbers of VNTR.
  • VNTR is specific from person to person.
  • The size of VNTR varies from 0.1 to 20 kb.
  • Any difference in the nucleotide sequence (inheritable mutation) observed in a population is called DNA polymorphism (variation at genetic level).
  • Polymorphism is higher in non-coding DNA sequence because mutations in these sequences may not affect an individual’s reproductive ability. These mutations accumulate generation to generation causing polymorphism.
  • Polymorphisms have great role in evolution & speciation.
Steps of DNA fingerprinting (Southern Blotting Technique)
  1. Isolation of DNA (from any cells or blood stains, semen stains, saliva, hair roots, bone, skin etc.).
  2. Digestion of DNA by restriction endonucleases.
  3. Separation of DNA fragments by gel electrophoresis.
  4. Transferring (blotting) DNA fragments to synthetic membranes such as nitrocellulose or nylon.
  5. Hybridization using radioactive labelled VNTR probe.
  6. Detection of hybridized DNA by autoradiography.
The autoradiogram gives an image in the form of dark & light bands. It is called DNA fingerprint.


  • DNA fingerprint differs in everyone except in monozygotic (identical) twins.
  • The sensitivity of the technique can be increased by use of polymerase chain reaction (PCR). Therefore, DNA from a single cell is enough for DNA fingerprinting. 
Application of DNA fingerprinting: 
  • Forensic tool to solve paternity, rape, murder etc.
  • For the diagnosis of genetic diseases.
  • To determine phylogenetic status of animals.
  • To determine population and genetic diversities.

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