DNA FINGERPRINTING

DNA FINGER PRINTING:

  • DNA finger printing is a very quick way to compare the DNA sequences of any two individual.
  • DNA fingerprinting involves identifying differences in some specific regions in DNA called repetitive DNA, because in these sequences, a small stretch of DNA is repeated many times.
  • During centrifugation the bulk DNA forms major peak and the other small peaks are called satellite DNA.
  • Depending on base composition (A:T rich or G:C rich), length of segment, and number of repetitive units, the satellite DNA classified into many types, such as mini –satellite and micro – satellite.
  • These sequences dose not code for any proteins.
  • These sequences show high degree of polymorphism and form basis of DNA fingerprinting.
  • Polymorphism in DNA sequence is the basis of genetic mapping of human genome as well as of DNA fingerprinting.
  • Polymorphism (variation at genetic level) arises due to mutations.
  • If an inheritable mutation is observed in a population at high frequency it is referred as DNA polymorphism.

The process:

  • DNA fingerprinting was initially developed by Alec Jeffreys.
  • He used satellite DNA as the basis of DNA fingerprinting that shows very high degree of polymorphism. It was called as Variable Number Tandem Repeats.(VNTR)
  • Different steps of DNA fingerprinting are:-
    • Isolation of DNA.
    • Digestion of DNA by restriction endonucleases.
    • Separation of DNA fragments by gel electrophoresis.
    • Transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon.
    • Double stranded DNA made single stranded.
    • Hybridization using labeled VNTR probe.
    • Detection of hybridized DNA fragments by autoradiography.

  • The VNTR belongs to a class of satellite DNA referred to as mini-satellite.
  • The size of VNTR varies from 0.1 to 20 kb.
  • After hybridization 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.
  • The DNA from a single cell is enough to perform DNA fingerprinting.

Applications:

  • Test of paternity.
  • Identify the criminals.
  • Population diversity determination.
  • Determination of genetic diversity.

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Transcription is a process where DNA is converted into RNA by the help of RNA polymerase. Information of DNA is copied into mRNA for the synthesis of protein. After RNA synthesis it is modified further by the process of post transcriptional modification.

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Translation is a process of synthesis or formation of protein from mRNA. Three process like initiation, elongation and termination are involve in translational process.

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Replication is a process of copying of DNA. Messelson and stahl done an experiment to prove that DNA is of semi-conservative in nature where one strand is antisense or template strand and other strand is sense or leading strand.

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Genetic material was searched by the help of following experiments. Frederick Griffith done an experiment on streptococcus pneumoniae to recovered genetic material. Avery, Mccarty and Macleod identify the biochemical nature of genetic material.

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DNA is tightly packed in the nucleus of every cell. DNA wraps around special proteins called histones, which form loops of DNA called nucleosomes.

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Expression of genes can be regulated by lac operon model which was proposed by Jacob and Monad. The regulation of lac operon by repressor is known as negative regulation.

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