DNA printing Or profiling or typing

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DNA printing Or profiling or typing

• DNA printing compares sets of DNA by locating
  identical sequences
• of nucleotides called repetitive DNA, often
  for the purposes of forensic identification.
• DNA finger printing was invented by British
  geneticist Alec Jeffreys.

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Principle of DNA finger printing

• DNA finger printing is based on the fact that DNA
  of one individual is about 90 identical to the
  DNA of another individual, but there is 10 of
  DNA that is different from others.
• This 10 of the total DNA is important, it does
  not code for any protein or RNA.
• It carries some specific short sequences.
• The specific sequences are tandem repeated many
  times and are present throughout the length of
  DNA.
• These repetitive DNA s are more in satellite part
  of a chromosome, or in Kinetochore, or in nuclear
  organizing regions.
• The number of repeats is very specific in each
  individual, and it is inherited.

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POLYMORPHISM IN DNA.

• The number of repetitive sequences present at one
  locus of an individual differ from the number of
  repetitive sequences present in the other locus
  of the same individual, and the repetitive
  sequences are with different number of nucleotide
  base pairs. This phenomenon is called
  polymorphism.
• Where as the other individual is likely to have
  different numbers of repeats at these loci.
• Polymorphic genetic loci are called simple
  tandem repeats.
• Tandem repeats of short sequences are called
  Variable number tandem repeats.

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Sources of DNA for finger printing.

• From blood, semen stains, saliva residues, tissue
  bits, or even hair follicle.

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Steps involved in DNA finger printing technique.

• 1.Isolation of DNA
• 2. Digestion of DNA by Restriction Endonucleases.
• Separation of DNA by electrophoresis.
• Transferring of DNA separated fragments to
  synthetic membranes such as nitrocellulose or
  nylon.
• Hybridization using labeled VNTR probe.
• Detection of hybridized DNA fragments by
  autoradiography.

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Isolation of DNA

• DNA molecule is isolated from the source by high
  speed refrigerated centrifuge.
• Bulk DNA forms a major peak, small peaks are
  formed by satellite DNA.
• Alec Jeffreys used satellite DNA as a probe.
• Satellite DNA are of two types. One is mini
  satellites, and micro satellites. Based on number
  of base composition, length of segments and
  number of repetitive units.

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Amplification of DNA

• If the amount of DNA available is less, the
  available DNA is amplified to increase the amount
  of DNA by polymerase chain reaction (PCR).

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Digestion of DNA with restriction endonucleases

• Endonucleases are called molecular scissors.
• They splice the DNA at a specific site.
• They cut the DNA at specific sites.

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Separation of DNA by Gel electrophoresis.

• It is the method used to separate the DNA
  fragments based on their charge to mass ratio.
• It requires a glass vesssel called well. The
  contains polyacrylamide solution.
• The DNA fragments move towards anodes based on
  their charge to mass ratio.
• Fragments with low charge to mass ratio move
  downwards towards anode.
• The various fragments form bands.

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Transferring of separated DNA strands on to
synthetic membranes.

• After separating DNA fragments by
  electrophoresis, the fragments are transferred on
  to synthetic membranes like Nitrocellulose or
  Nylon by a technique called Southern blotting
  technique.

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DNA probe.

• DNA probes are repeated sequences of DNA
  complementary to those present in VNTRS.
• These probes are made radioactive.
• The radioactive DNA probes bind with the
  repetitive sequences on the nylon sheet. This is
  called hybridization.

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Autoradiography.

• An X ray film exposed to the nylon sheet to mark
  the places where the radioactive DNA probes have
  come to bound to the DNA fragment. These places
  are marked as dark bands when X-ray film is
  developed. This process is called
  autoradiography.
• The dark bands represent the DNA finger prints or
  the DNA profiles.

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Applications of DNA technology.

• In settling the paternity disputes, that is in
  determining of biological father of child.
• In detecting criminals.
• In ascertaining of an immigrant under scrutiny c

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