Every organism has unique DNA sequences just like each individual has got unique finger print. In forensic science individuals are identified by scanning for 13 DNA regions, that vary from person to person and they use this information to create DNA profile or DNA fingerprint of that particular individual. There is very little possibility of another person having the same DNA profile or DNA fingerprint for this particular 13 DNA regions.
At present identifying each individual belonging to same species is little bit less precise, but as the technology of DNA sequencing progresses, comparison of large part of genome or DNA fragment or even the whole genome will become feasible, easy and also precise in identifying individuals belonging to the same species.
Procedure for DNA Sequencing:
In Criminal Case:
1) Forensic scientists will collect samples like blood, hair, bone or any other body organs or tissues from the crime-scene and also from the suspect
2) Next step will be extracting the DNA and studying or analyzing the DNA for the presence of specific DNA regions in specific pattern.
3) Forensic scientists with the help of small DNA sequences also known as DNA probes try to identify the DNA regions of the sample. These DNA probes are single stranded and are the sequence is complementary to the sample. A number of probes which are complementary to the DNA sample will bind and creates unique pattern for every individual.
4) If DNA samples from the crime spot and the suspect form the same pattern it indicates that the suspect is the person who committed that particular crime.
5) If the DNA patterns are different then the suspect is not involved in the crime.
Techniques Used In Forensic Investigation:
Restriction Fragment Length Polymorphism (RFLP):
RFLP is used to analyze the different sizes of DNA fragments obtained as a result of DNA digestion with restriction endonuclease enzymes. These restriction endonuclease enzymes cut the DNA at specific sequence also known as restriction endonuclease recognition site (palandromic sequence). Depending on the presence of these recognition sites in a DNA sample produces different lengths of DNA fragments. Electrophoresis technique is used to separate all these different lengths of DNA fragments. After the separation DNA probes are allowed to hybridize with the complementary DNA fragments in the sample.
Now a day due to the advances in the technique RFLP is not used as much as it was used few years ago in the forensic investigation.
Polymerase Chain Reaction (PCR):
PCR technique used to amplify small quantity of the DNA sample from the crime scene. PCR can amplify and analyze DNA from small biological samples like few cells of a tissue.
Short Tandem Repeats (STR):
STR is present in the nuclear DNA or genome of an individual. STR variability are also used by FBI (Federal Bureau of Investigation) to identify criminals, offenders or missing individuals using the national DNA profile database.
Mitochondrial DNA is a circular DNA present in a cell organelle known as Mitochondria. Mitochondria or Mitochondrial DNA is passed from one generation to the other as maternal inheritance. Therefore this technology can be used in identifying maternal relatives and also can be used in missing-person investigations.
Y-chromosome is sex specific that is they are only present in males and are inherited directly from father to son. Therefore analyzing the DNA segments in the Y-chromosome can be used in solving paternal disputes.
Forensic department were able to solve so many cases using all these new techniques, and also they have designed forensic DNA database, which will further accelerates the process of solving mysterious crime.
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