January 11, 2011

Role of recombinant DNA technology in Forensic Sciences

Volume 2, Issue 2
THE RECOMBINANT DNA technology helps the human beings in investigation system to fight against crime and sort out civil disputes. This technology is much important because criminals use quite sophisticated and modern gadget and arsenal. In such circumstances, DNA fingerprinting could help in identifying them. Whenever a person commits a violent crime such as rape or murder, there is a good chance that he or she will leave behind small amounts of skin, blood, saliva, semen, hair, nails etc at the scene of the crime or on the body or clothes of the victim. The modern forensic scientist can extract the tiny amount of human DNA present in such biological clues (crime stains) left behind by the criminal. This trace amount of DNA is amplified in quantity and analyzed in the lab to find out the genotype of the crime stain.

The traditional approach was through the use of morphological and physiological features of different individuals to conduct population genetic studies. The numbers of scorable morphological characters are very few as compared to the biologically active genes. Moreover, eukaryotic genome has large amounts of repetitive DNA that is not expressed and does not contribute to the morphological or physiological appearance. In case of very closely related individuals and species, there are very few morphological differences, which as a matter of fact do not represent the true genetic differences at the DNA level. Thus, there is always a need to study polymorphism at DNA level. This constitutes human DNA typing of the criminal and provides the investigator with a “genetic identity” or DNA fingerprinting of the criminal.

The chemical structure of every organism’ DNA is the same. The only difference between organisms is the order of the basic pairs. There are so many millions of base pairs in each individual’s DNA that every individual has a different sequence. Using these sequences, every organism could be identified solely by the sequence of their base pairs. These sequences variations may be exploited to find polymorphisms among individuals. The polymorphisms among the individuals are the bases of DNA fingerprinting. In general, DNA fingerprinting is a method for genetically identifying an individual and defining their genetic relationship to other individuals OR distinguishing individuals with DNA analysis is called DNA fingerprinting or DNA typing. Hence forensic medicine can be defined as “The knowledge and techniques of medical science applied to assist in the solution of crimes, legal disputes etc is called Forensic Science or Forensic Medicine. Establishing the identity of victims (e.g. of murder, accidents etc), criminals (e.g. in cases of rape, murder etc) father (in cases of paternity dispute) etc is critical to solve the problems of crimes/cases.

The DNA from a biological sample left at the scene of a crime can be analyzed and compared with the DNA of likely suspects. A match between evidence and a particular individual is helpful to the prosecution. In addition, DNA comparisons are used to determine whether individuals have been wrongly convicted of a crime.

Techniques Involved in DNA Fingerprinting

Generally there are two approaches / techniques for determining DNA relationships among humans.

(1) DNA Hybridization:-

This approach relies on DNA hybridization to undegraded minisatellite DNA. It is called restriction fragment length polymorphism (RFLP). It is applied to study evolution, population genetics, phylogenetic relationships and genome mapping, but it needs large and good quality genomic DNA. Moreover, the process is time consuming and requires radioactivity for detection.

RFLP analysis consisted of DNA isolation, digestion of the DNA with a suitable restriction enzyme, separation of the restriction fragments by agarose gel electrophoresis, transfer of the separated restriction fragments to a filter by southern blotting, detection of individual restriction fragments by nucleic acid hybridization with radioactive / non-radioactive labeled cloned probes, and scoring of RFLPs by direct observation of autoradiogram.

Because of the extensive variability in human minisatellite DNA sequences, the chance of finding two individuals in the population with the same DNA fingerprinting is about one in 10,00000 to 10,00000000. Therefore, an individual’s DNA banding pattern based on minisatellite DNA sequences is almost as unique as his or her fingerprints.

(2) Polymerase Chain Reaction (PCR):-

To overcome the limitations of RFLP, new PCR-based diagnostic marker assays were developed. These are called arbitrary primed PCR (AP-PCR), Random amplified polymorphic DNA (RAPD) and also DNA amplification fingerprinting (DAF). The use of PCR amplification for STR (Short tandem repeats) sequence analysis is faster, much more convenient and highly reliable.

The PCR methods have the following advantages:

(i) It is very sensitive and it can generate results from the very minute amounts of DNA obtained from even such specimens as hairs and saliva stains on cigarette butts.

(ii) The results are obtained rather quickly

(iii) PCR analysis could be done even when DNA is fragmented into short lengths e.g. DNA from bones that have been buried for many years.

In Pakistan, The Punjab government has been fully supporting University of Veterinary and Animal Sciences (UVAS) to take initiatives in forensic sciences because the technology can revolutionize investigation system to fight against crime and sort out civil disputes. UVAS has the best forensic lab to conduct analysis of meat beef and solving animal theft cases and ownership disputes by modern forensic DNA technology. Some of the basic techniques of forensic DNA typing have also been established at CAMB, Lahore by amplifying a forensically information locus from human genomic DNA.

http://www.technologytimes.pk/mag/2011/jan11/issue02/role_of_recombinanat_dna.php

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