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DNA printing Or profiling or typing

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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DNA printing Or profiling or typing

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  1. 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.

  2. 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.

  3. 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.

  4. Sources of DNA for finger printing. • From blood, semen stains, saliva residues, tissue bits, or even hair follicle.

  5. 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.

  6. 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.

  7. 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).

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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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