DNA Typing or DNA Profiling or DNA Fingerprinting

DNA Fingerprinting- Process and Application:

dna fingerprinting technique - DNA Typing or DNA Profiling or DNA Fingerprinting

DNA fingerprinting was discovered by Sir Alec Jeffreys in 1985.

DNA fingerprinting is a well-known method of identifying criminals by the means of their digital/palmer prints.

DNA fingerprinting is a technique to find out variations in individuals of a population at the DNA level.

DNA fingerprinting works on the principle of polymorphism in DNA sequences.

Process of DNA Fingerprinting:

Source of DNA:

The DNA is extracted from the nuclei of whatever evidence is available for example from white blood cells in case of a blood sample or from hair follicle cells that cling to the roots of hair that have fallen or have been pulled out, or from spermatozoan’s in the semen sample.

DNA Amplification:

If the content of DNA is limited, DNA can be amplified by making many copies of it using PCR or Polymerase Chain Reaction.

Fragmentation:

The DNA sample is digested by a restriction enzyme which cuts the DNA into fragments at specific sites to separate VNTRs (Variable Number Tandem Repeats). The number of these sites present in an individual’s DNA dictates the number and size of DNA fragments generated by the enzymes.

Separation of VNTRs:

These fragments are separated by gel electrophoresis set up containing agarose polymer gel. The separated VNTRs can be visualized by staining them with a dye that fluoresces under ultraviolet radiation.

Single Stranded DNA:

Double-stranded DNA is then split into single-stranded DNA using alkaline chemicals.

Southern Blotting:

These separated DNA sequences are transferred to a nylon or nitrocellulose sheet placed over the gel. This is called ‘Southern Blotting’.

DNA Probes:

They are small radioactive synthetic DNA segments of known sequences of nitrogen bases.

Hybridisation:

The nylon sheet is then immersed in a bath and probes or markers that are radioactive, synthetic DNA segments of known sequences are added. The probes target a specific nucleotide sequences which is complementary to VNTR sequences and hybridizes them.

Exposure to X-ray Films:

Finally, X-ray film is exposed to the nylon sheet containing radioactive probes. Dark bands develop at the probe sites which look something like the bar codes used to identify items at the grocery store.

The degree of variation is so high that every individual with the exception of identical twins, produces a unique band pattern, as every individual has a unique set of ordinary fingerprinting.

Identity of a criminal is determined by comparing the accused man’s DNA with that of the blood or seminal stain found at the scene of the crime. If the DNA fingerprintings are identical, there is an absolute identification.

Applications of DNA Fingerprinting:

DNA Fingerprinting is used to-

  • Identity criminals in forensic laboratories.
  • Determine paternity.
  • Verify whether a hopeful immigrant is a really close relative of already an established resident.
  • Identify racial groups to rewrite biological evolution.

Important Terms:

Transcription:

  • It is the formation of mRNA (Messenger RNA) from DNA in the process of protein synthesis.
  • It takes place in the presence of enzyme-RNA polymerase.
  • One of the strands of DNA acts as a template to direct the synthesis of mRNA.
  • In bacteria, the transcribed mRNA is functional but in eukaryotes, the gene is split and exons are interrupted by non-coding sequence, introns which are removed.

Polymorphism:

  • It means variation at genetic level which arises due to mutations.
  • The polymorphism in the DNA sequence is the basis of the genetic mapping of the human genome as well as DNA fingerprinting.
  • The allele sequence variation is called DNA polymorphism if more than one variant (allele) at a locus occurs in the human population.
  • The probability of such variation to be observed in the non-coding DNA sequence is higher as mutations in these sequences may not have any immediate effect. These mutations keep on accumulating in each generation and form one of the basis of polymorphism.
  • It has an important role in evolution and speciation.

Translation:

  • It is the synthesis of protein in the cytoplasm of the cell due to coded information carrying from DNA through mRNA.
  • It occurs on the ribosomes using mRNA and tRNA (Transfer RNA).
transcription and translation - DNA Typing or DNA Profiling or DNA Fingerprinting

Bioinformatics:

  • It is the discipline in which the database of biological information is created and maintained.
  • Bioinformatics is the field in which information science is applied to biology.
  • The huge amount of genomic sequence information has been generated through years of research.
  • Most of this information is in the form of sequence, images, intensities, and structures.
  • The representation, modeling, and simulation of biological systems are dealt with, at an advanced level, in bioinformatics.
  • Bioinformatics throws light on the evolution of several species on the earth and helps mankind to unearth the several mysteries of genetics.
  • Bioinformatics is increasingly being utilized in pharmaceuticals, textiles, agricultural and biotech companies.
  • The most remarkable success of bioinformatics to date has been its use in the ‘shotgun sequencing‘ (breaking of a large piece of DNA into smaller fragments) of the human genome.
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