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DNA and Forensic Science

 
The double helix that represent the personal information in human genetics.
Source: www.forbes.com

Nearly two decades ago, the general public found the word or acronym of DNA is a strange term in their lives. There are only a few groups of people that have been exposed to this term and know about it. The term of DNA is becoming popular in Malaysia due to a trial of a high profile case in the court of justice in late 90s.

To date, various descriptions and exposures on DNA in printed media and even electronic increase the knowledge of the members of the community about DNA.

Introduction to DNA

DNA or deoxyribonucleic acid is the key components of life. It contains sets of biological instruction that make up the personality of the individual. This information was passed on from generation to generation through the reproductive development. (National Institute of Health, 2013).

All life on this earth has a unique DNA pattern: to make a man’s man and a tiger is a tiger.

A human would have a complete set of chromosomal DNA derived from his mother and father. It is a set of 23 pairs, each of which is from the mother and the father makes the total number of 46 sets of chromosomes. (American Prosecutors Research Institute, 2003).

These sets of chromosomes are lined by millions of information about his life as a man. This information is known as genes. Examples of such genes are can be detected in a form of variation eye colour or nose. (American Prosecutors Research Institute, 2003).

Where is the DNA in the body?

Do you know where we can find DNA in our body?

DNA can be found in the nucleus. It is located in the nucleus of cells that form the tissues and organs of the body. Apart from the cell, DNA is also available in the mitochondria.

What are examples of cells with the DNA chain?

DNA can be found in every cell as below except red blood cell:

  • White blood cell
  • Sperms
  • Vaginal secretions
  • Mucus
  • Sweats
  • Saliva
  • Ear’s wax
  • Hair roots
  • Bones
  • Tooth

It can also be obtained from organs such as the heart and liver, and muscle tissue of the skin.

In an ordinary circumstance, the DNA will be extracted from the nucleus and analysed to obtain it sequence for comparison. However, in cases involving decomposed bodies or where the sample is too small, mitochondrial DNA is more appropriate compared with nucleus DNA.


A relationship between cell and nucleus in human body.
Source: http://ocw.mit.edu/

Applications of DNA in Forensic Science

After the successful attempts in revealing the mystery behind the human DNA and its sequences, scientist learnt that DNA is a unique characteristic in the variation of life. The DNA technology is then applied into the forensic investigations.  In most cases, the use of DNA is to identify the unknown identity for a decomposed body such as in a case of mass disaster. Besides that, it is also use to ensure the identity of a questioned baby in maternity or paternity testing.

When presenting a DNA related case in court of law, there are a few steps need to be followed by the scientist. These steps are as follows (American Prosecutors Research Institute, 2003):

  1. Identify the genetic profiling of the biological samples obtained from the scene (for example, sperm remains in the incidence of rape)
  2. Identify the genetic profiling of the biological sample obtained from the suspect.
  3. Make comparison between the two profiles (1 and 2) for the similarity or dissimilarity.
  4. Calculate the statistical probability in a population for a random individual genetic profiling to have such profile as collected from the scene.

Then, the prosecutor could use this information’s for the trial. Such information helps the court in determining the offender.

How a DNA profiling helps the investigation?

Apart from determining the probability of the similarity of the genetic profiles found at the scene and of the victim, DNA profiling is able to answer some other questions. Question such as ‘where is the DNA sample found’ and ‘what type of DNA sample found’ could help the investigators narrow down the scope of investigation (American Prosecutors Research Institute, 2003).

Example 1:

A woman claimed to be raped in a car belonging to a suspect. The victim’s DNA was found in the car seat altogether with the suspect’s DNA sample. The evidence gives a correlation between the woman and the suspect in the car, as stated by the victim.

Example 2:

A seminal stain was found in the victim’s vagina. The seminal stain is similar to the suspect’s DNA profile. Therefore, it gives the impression that there could be a sexual intercourse between them.

If in the victim’s testimony stating that she had scratched the suspect’s face; the suspect’s DNA could be found in the victim’s fingernails.

References

  1. American Prosecutors Research Institute. (2003, 11). forensic dna fundamentals. Retrieved 06 22, 2013, from http://www.ndaa.org: http://www.ndaa.org/pdf/forensic_dna_fundamentals.pdf
  2. Lister Hill National Center for Biomedical Communications et al. (2013, 06 17). Genetic Home Reference. Retrieved 06 21, 2013, from http://ghr.nlm.nih.gov: http://ghr.nlm.nih.gov/handbook/basics.pdf
  3. National Institute of Health. (2013, 06 13). National Human Genome Research Institute. Retrieved 06 21, 2013, from http://www.genome.gov: http://www.genome.gov/25520880

 

Last Reviewed : 17 October 2013
Writer : Khairul Adli b. Nikman
Accreditor : Dr. Shahidan bin Md Noor

 

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