Dna Profiling –a Forensic Tool

By valeri On August 3, 2010 Under Criminal Profiling

D6.7b: Workshop on Forensic ...




Every object, natural or manmade, has an individuality, which is not duplicated in any other object .It is unique. Neither the nature has duplicated itself, nor man can. This is the law of individuality, which is of fundamental importance in forensic science. Anything and everything involved in a crime has individuality. The culprit is unique, his modus operandi is unique, his weapon of offence is unique, scene of crime is unique, evidentiary clues, left over or picked up by the culprit, are unique. The main task of the investigator is to identify the uniqueness to link the crime with the criminal. It was a tedious task till the advent of the DNA Profiling technique .The advancement in biotechnology has gifted the forensic scientist with the most powerful genetic marker, the DNA, for individualizing and discriminating the biological evidence in forensic investigations. The term DNA Fingerprint was a trade mark name given by Cell mark Diagnostics, a company in America which licensed the technique, developed in U.K.Later this term was evolved to be replaced by the term DNA Profiling.DNA profiling is an absolute method for identification as on today for individualization of biological sample to the probability value of 99.9998 percent. The theory of the technique lies of the fact that each individual inherits DNA from its parents in the proportion of 50:50 DNA in one person does not match with other person in the world.


DNA stands for deoxyribonucleic acid which is found in the chromosomes of the cells of living beings is the blue print of an individual.DNA determines the characteristics of the person such as the color of the skin ,type of hair, nails and so on. Using this genetic fingerprinting identification of an individual is done like in the traditional method of identifying fingerprints of suspects. This method of identification provides hundred percent precision. Structurally, DNA is a double helix-two thread like long strand of genetic material spiraled around each other. DNA is a polymer of deoxyribonucleotides composed of Base [Adenine (A), Thymine (T), Guanine (G), and Cytosine (C)], Sugar and a Phosphate. The sequential arrangement of the individual nucleotides is responsible for giving uniqueness to any individual living form, be it humans, animals, plants, or microbes. The DNA fingerprinting technique was developed by Sir Alec Jeffreys of the Leicester University Sir Alec first made his world-changing discovery by separating strands of DNA into different sizes and showing them as bands on a photograph. What first seemed to him to be ‘a complicated mess’ has now become invaluable for police investigation, ranging from settling immigration and paternity disputes to solving rape and murder cases. He observed that while large sections of DNA show similar base sequence for every human being as they are made of same body components, a few sections of human DNA are found varying from individual to individual. This observable variation in human DNA is called polymorphism. These polymorphic segments in the DNA molecule serve as a means to identify individuals. To determine the individuality the DNA has to be first extracted from the specimen. The DNA is found in every living cell of our body, such as blood, semen, hair roots, bone, saliva, urine, a postmortem specimen etc.


The DNA is first extracted from a specimen by an elaborate chemical process. It is then mixed with a special enzyme called restriction endonucleasis which function as biological scissors which cut the DNA at specific sites .The restricted fragments are then separated according to size using gel electrophoresis technique. The fragments are put on a gel and electric current is applied. The shorter fragments move across on the gel faster towards the positive pole than the longer fragments. This separates the DNA fragments on the basis of their length. The next process is southern blotting. This process fixes the DNA fragments to the membrane firmly and in the same position. This is followed by hybridization process.Hybridisation involves bringing in contact a radioactive labeled probe , which is a particular type of DNA molecule that binds specifically with its complimentary base sequence present I the membrane. The probe bound fragments being

Radioactive can then be recorded on an X-ray plate .This process is known as autoradiography. The X-ray plate will show dark bands appearing very much like bar code. The comparison of the bands in the DNA profiles of different specimen from the same individual will show similarity whereas DNA specimen of two different individuals will show different DNA profiles. This is the DNA profiling technique. Most recently another technique known as polymerase chain reaction has been developed for DNA profiling. This method is recommended when there is insufficient DNA for analysis or is in degraded form. The PCR technique takes into account polymorphic DNA segments and through a polymorphic chain reaction produces multiple copies of a particular polymorphic DNA segment which would be sufficient to meet the requirements of DNA profiling test.


If the DNA fingerprint of a person matches with that of a sample, it means that the sample has come from that person only. The probability of two persons except identical twins having the same DNA finger print is around 1 in 30 billion world population it means that DNA test gives the perfect identity .It is a very advanced science.

The main advantage of this method is its ability to analyze very minute and environmentally challenged samples and to accurately establish their origins with a high degree of certainty .DNA is much resistant to degradation caused by environmental conditions like temperature humidity time which lead to the growth of micro organisms .It generates the same genetic pattern irrespective of the biological material like hair ,seminal stains, fresh blood, soft tissue, hard tissue etc.In fact this unique feature makes it a powerful tool in forensic identification. DNA can be successfully obtained fro blood and blood stains, vaginal and anal swabs, oral swabs, clothing, bone teeth, most organs and to some extent urine. Material objects obtained from the scene of crime like liquor bottles, glasses, cigarettes, stamps and envelope flaps have all been found to provide varying amounts of DNA .This helps in linking the suspect with the crime scene.

Difficult problems connected with sexual offences can be solved by DNA profiling test. The vaginal swabs ,seminal stains and blood stains can be subjected to DNA technique for identifying the rapist or excluding the suspect with near certianity.In homicidal crimes , assault, hit and run accidents any type of body sample may be found at the crime scene such as hair ,teeth, saliva etc, though DNA may be insufficient in hair or saliva specimen by the application of the PCR technology, the offender can be identified.DNA profiling is used in identifying dead bodies in mass disasters, accidents etc.Likewise postmortem tissues or organs of the deceased can be identified by DNA test to establish the likely parentage of the deceased . DNA profiling is used in resolving paternity dispute which involve issues like maintenance suits, inheritance disputes or immigration problems. This technique has been used in Britain to screen immigrants claiming citizenship on the basis of their relations holding British citizenship. Cases which were closed due to lack of evidence can be re opened in the light of the DNA profiling technique.



Modi’s Medical Jurisprudence-22nd Edition, page 540 to 542.

Taylor’s Principle and Practice of Medical Jurisprudence.

Pantangi Balarama Venkata Ganesh v. State of A.P. 2003 CRI.L.J.4508.


Article Source: http://www.articlesbase.com/science-articles/dna-profiling-a-forensic-tool-531196.html

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10 Comments Add yours

  1. Nikki B
    March 21, 2009
    6:28 am

    Is criminal Profiling part of criminology or Forensic profiling? and which uni is best for it?
    im finishing school and i would like to know if criminal profiling is part of criminology or forensic psychology. I would also like to know which uni is better for it. I don’t mind international universities either. This is because i would like to become a Australian Federal Police Agent.


  2. sinister_miss_nancy
    July 2, 2009
    6:16 pm

    Careers in forensic science or criminal profiling?
    Can you help me with the pros/cons of careers in A:Forensic Science/CSI and B:Criminal Profiling.

    I would like to go into one of these careers but not sure which. If someone could either help me on here that would be great, and I would appreciate any books/sites where I can research this.
    Thanks in advance guys!

    • Anonymous
      September 28, 2010
      11:00 pm

      look under the harris county sheriffs office, i know you dont live there, but they tell you about all the different aspects

  3. sienna grace
    September 3, 2009
    7:43 pm

    what books can i get about forensic science and profiling?
    i’d like to become an fbi agent and work in the BAU [ behavioral analysis unit ] the whole thing really interests me and even though i’m only a sophomore in highschool, i’d like to start reading about it now.
    so any good books/websites/anything i can get online maybe about:
    forensic science
    criminal physcology
    and some schools that would be good for this field.

    • Anonymous
      September 28, 2010
      11:00 pm

      There are many on google. Just any of them which suits you.

  4. wufpakfan0915
    February 27, 2010
    7:31 pm

    Is it possible to do criminal profiling without a forensic psychology degree?
    I have always wanted to do criminal profiling because I really enjoy psychology but also criminal justice but the problem is the only way I know how to do this is with a degree in forensic psychology and that I know of there are not any colleges semi-close to me(NC) that offer this form of psychology. I was wondering if there was any other way to do this like majoring in a specific form of psychology and minoring in criminal justice or something of the sort,

  5. H
    July 1, 2010
    9:01 pm

    I am wondering about Forensic Profiling?
    I am very interested in forensic psychology and profiling. But I am not too sure which area I would like to go into. So I was looking for some more information on both fields. Also what sort of minor and major I should go after.

    • Anonymous
      September 28, 2010
      11:00 pm

      A forensic psychologist typically holds dual degrees in law and psychology. Criminal and civil careers are available for forensic psychologists. The primary task of any forensic psychologist is to provide psychological insight on legal matters. A forensic psychologist may help a judge determine competency, a prosecutor choose a jury, provide expert witness testimony, work with authorities as a criminal profiler or review case files of defendants pleading insanity.
      In forensic psychology, the mental condition of a defendant is admissible if he or she is trying to avoid trial based on an inability to stand trial for the crime committed. In most cases, a forensic psychologist interviews the defendant and reviews his or her medical records and case history. Finding a defendant incompetent to stand trial may result in the defendant’s commitment to a mental health facility to receive treatment. Forensic psychologists brought in by the prosecution, the defense and the court can argue their expertise and evaluation of the defendant’s mental state along with an understanding of the legal definition of incompetence.
      As an expert witness, a forensic psychologist may be brought in independently to evaluate a defendant’s state of mind under the McNaughton rules. McNaughton states that a defendant must be able to tell right from wrong in order to be held accountable for his or her actions in criminal proceedings. If a defendant is legally incapable of determining right from wrong, he or she may plead not guilty by reason of insanity or mental defect. Forensic psychologists need a deep understanding of the legal and psychological ramifications. While mental illness is determined as any state affecting mental health (such as depression or bipolar disorder), the legal definition of insanity is radically different. Forensic psychologists understand that insanity is a legal, not medical term.
      Expert Witness
      As an expert witness, a forensic psychologist provides expertise to the court. Forensic psychologists may weigh in on the welfare of a child in child custody cases. They may evaluate eyewitness testimony in order to help guide attorney questioning. Forensic psychologists can help judges determine whether parental disputes over child custody have founding in reality. They can also help smooth the questioning of minors to determine any patterns of emotional, physical or mental abuse. As experts, forensic psychologists’ independent testimony can sway judges and juries.
      Criminal Profilers
      Criminal p0rofiling is one of the more glamorous and advertised areas of forensic psychology. Most forensic psychologists who go into criminal profiling have extensive education (doctorate degrees in law and psychology). Criminal profilers help law enforcement detail a person or persons behind certain types of crimes. For example, forensic psychologists use their expertise to profile serial killers to help police narrow down their suspect pool. Criminal profilers may also be called on to provide a psychological profile of suspects and defendants in criminal proceedings. In addition, criminal profilers provide insight on racial, economic and ethnic profiling for federal and local agencies.
      Jury Consultant
      Jury consultation is a less glamorous but lucrative career for forensic psychologists. Both prosecuting and defending attorneys bring in jury consultants (particularly in high-profile cases) to help attorneys analyze the potential pool of jurors, providing insightful questions and eliminating jurors for various reasons (from body language to verbal cues). Jury consultants may work with an attorney throughout the length of a trial helping to identify what portions of the attorney’s message is reaching the jury and what areas are not.
      Forensic Psychology
      With many different subspecialties, forensic psychology presents many career opportunities. For people who like working with others and making a real difference in the lives of offenders and victims alike, forensic psychology can be a rewarding career choice.

      The drawbacks to a career in this area are the needs for constant updates to education (seminars and conferences) and two separate degrees. Forensic psychologists work long hours and in potentially dangerous situations (particularly if working heavily in criminal court or in a prison). Forensic psychology is a high-stress career field with a risk for burnout.

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