Abstract
This research paper will discuss the significant contribution of DNA fingerprinting in the criminal justice system for being able to provide a reliable basis for conviction. DNA fingerprint analysis is referred as an accurate indicator to determine the guilt and innocence of an accused. The history, importance and various DNA fingerprinting techniques shall be discussed. In addition, DNA fingerprinting is considered as more superior than other forensic science methods since the technology has improved over time. DNA fingerprinting has allowed the test of smaller amounts of material, faster testing procedures and more conclusive results. Finger ridge analysis is science and cannot be flawed since what can be seen by the naked eye can be verified by forensic science. It has become an acceptable and a reliable method that deals with identification of individuals during crime scene investigations.
Introduction
Newton (2004) explained that DNA fingerprinting has become a permanent process that has been accepted by society as a method to prove the innocence or guilt of the accused in criminal cases, and clarifying paternity. In fact, DNA fingerprinting has been regarded by law-enforcement officials as one of the most significant revolution in forensic science (Garfield, 1989). DNA fingerprinting can also be used in paternity testing and other biological applications. The individual-specific genetic fingerprints can be obtained from samples taken from the human body such as blood, a strand of hair, semen, and skin cells (Garfield, 1989). The flexibility of the fingerprinting process makes it an ideal technique during criminal prosecutions and forensic investigations. Although there are some who oppose that the DNA fingerprinting may violate protected freedoms under the Constitution such as the right against self-incrimination and the invasion of privacy, evidence is still obtained and presented in court to identify alleged perpetrators.
History of DNA Fingerprinting
According to Newton (2004), the first fingerprint research went down in various blind routes that had to undergo tandem repeat DNA in the human genome. It was inside Professor Jeffreys’s lab that resolved the human copy of the myoglobin gene that produced the oxygen carrying protein in muscle. Initially, the grubby mess of the first fingerprint was refined into clean patterns where DNA fingerprints which are unique in every person can be clearly deciphered. Lach & Patsis (2006) explains DNA or known as deoxyribonucleic acid that contained a specific sequence of bases known as nucleotides. These nucleotides hold the information of all the characteristics of living organisms. Such DNA information is inherited from the parents. DNA can be found in each cell of every living organism (Lach & Patsis, 2006).
Types of DNA Test Methods
Polymerase Chain Reaction (PCR)
One of the techniques of DNA printing is called the polymerase chain reaction (PCR) which was initially discovered by Kary Mullis in 1986 (Coyle & Schieman, 2007). This method became the foundation component of the majority of techniques used in DNA fingerprinting.
The PCR is the improved process that is able to generate an ample copy number of the DNA region of interest, or target, allowing for the detection of a specific DNA sequence in a sample that may be used for further analysis using other methods such as DNA sequencing (Coyle & Schieman, 2007). Due to the intricacies of forensic science, the DNA expert must be able to recognize the full significance of a suspect who may be sharing the same DNA profile as the one that was left at a crime scene. Hence, to be able to communicate the significance of a suspect being included as a donor of a DNA sample, the expected frequency of that genotype in the human population should be computed and reported as a random match probability (Coyle & Schieman, 2007).
With PCR, there is a need for the replication of genomic DNA that will need various enzymes such as the helicase, gyrase, RNA polymerase, and DNA polymerase, aside from the ribonucleotides and deoxy-ribonucleotides (Coyle & Schieman, 2007, p.24). The nucleotides are the building blocks or also known as the raw materials used for the formation of short strands of RNA primers, after they develop to newly synthesized and longer strands of DNA. The purpose of the helicase and gyrase is to separate and relax the duplex strands of DNA which contains each chromosome. This is now known as the condensed “package” of DNA which has been derived at birth. Such method made it possible for the RNA polymerase to combine to become single DNA strands and produce short segments of complementary RNA. The outcome of this method becomes a hybrid duplex that is composed of one strand of DNA and one strand of RNA with a free 3-hydroxyl assembly (Coyle & Schieman, 2007, p.27). Such hybrid duplex with its free 3-hydroxyl group is the target needed by the DNA polymerase, which has been identified as a DNA synthesizing enzyme. Thereafter, the DNA polymerase hits its target and moves toward a 5 to 3 direction. With this movement, there will be a creation of the suitable deoxy-nucleotide that will be added to the increasing chain that complements the existing nucleotide of the opposite strand (Coyle & Schieman, 2007). The end result will be a double-stranded DNA molecule that is a combination of one old strand and one new strand.
The process of PCR amplification of segments of DNA covers three main steps. The first step is the separation or the denaturation of the DNA double helix at high temperature, which is usually 95 degrees Celsius. The second step involves the annealing of short complementary DNA primer sequences which will determine the specific region of DNA to be amplified that has to be at least 50 to 65 degrees Celsius. The third step is the synthesis or extension that has to be at least 72 degrees Celsius. This will mark the completion of the amplification process for a single cycle of PCR (Coyle & Schieman, 2007).
DNA Sequencing
This method of DNA testing is the most current among the techniques. It is called the DNA sequencing, which is considered as a variation on the PCR theme or the PCR primer extension reaction that has three main differences. The first has only one oligo-primer which is being used in the reaction, which resulted to the primer extension having only one of the two strands of the double-stranded DNA template (Coyle & Schieman, 2007, p.28). The second main difference is that there is a need for a bigger amount of template. In the case of the PCR, the starting copy number of target DNA molecules must be more than 1,000 in order to derive microgram quantities of the final product. In DNA sequencing, there is an estimate of 5 times 10 copies of target molecules in order to generate a good quality of fluorescent signals in order to comprehend the targeted DNA. Hence, the PCR reaction must first be completed in order to generate a sufficient amount of templates needed for direct sequencing, or the process of cloning that will be succeeded by the sequencing of the clone (Coyle & Schieman, 2007, p.28). The last main difference is the inclusion of the dideoxy-ribonucleotides, which have been fluorescent labeled, together with the standard deoxy-ribonucleotides. The dideoxy-ribonucleotides have been identified to serve two purposes. In terms of the chemical process, the term dideoxy refers to the nucleotides that have a hydrogen atom attached to the 3-carbon of the sugar, rather than the hydroxyl group of the standard deoxy-nucleotide (Coyle & Schieman, 2007). The first function in the reaction is to act as the DNA chain terminator. The second function deals with the fluorescent tagging or labeling. With such label or tag, it becomes the signal that is easily identified in the event that it has been provoked by an ample energy source that may come from a laser. DNA cannot be seen by the naked eye. Hence, the fluorescent label shall enable the detection of each nucleotide base.
Amplified Fragment Length Polymorphism (AFLP)
This type of DNA that is called Amplified Fragment Length Polymorphism or AFLP is a very useful method that is used to genotype individuals of species that has small amount or no genome sequence data that is available. The AFLP initially creates the fragments by enzyme digestion at specific DNA sequence sites, which is different from the RAPD method. In RAPD, the process will generate directly from PCR the number of different length DNA fragments that will come from an individual by using six-base long primers. This type of fragment generation does not dependent on any of the factors which may influence the PCR efficiency. At the same time, such technique is less sensitive to slightly variable reaction conditions, which makes it easier to reproduce. The AFLP method will initially treat the genome with identified DNA restriction enzymes and cuts them into a consistent set of fragments (Coyle & Schieman, 2007). Thereafter, the DNA linkers or the double-stranded DNA shall be connected and linked to the ends of these fragments. As a result of the attached linkers, the fragments will now have the same two 20–30 base pairs of DNA sequence and will be amplified with just only two particular oligo-primers (Coyle & Schieman, 2007).
Short Tandem Repeats (STRs)
This type of DNA technique uses the tandemly repeated DNA units of mini- and microsatellite loci are often very useful for genotyping on the basis of the high level of polymorphic variation in a population (Coyle & Schieman, 2007, p. 39). The microsatellite sequences, which have been popularly known as short tandem repeats or STRs have a repetitive unit of two to six bases in length. They are then replicated in a tandem or head-to-tail direction. This discovery is based on previous studies where the genomic DNA was first isolated and then later on fractionated by application of concentrated gradients (Coyle & Schieman, 2007). After which, the fractions shall undergo analysis using spectrophotometry, and then every density of the fraction shall be plotted against their absorbency assessments. It was revealed that the bulk of the genomic DNA was taken from one fraction and produced the major absorbance peak. However, one or more secondary, or satellite absorbance peaks were also discovered. These fractions contained AT-rich repetitive DNA sequences that are generally connected with the centromere or telomere regions of chromosomes (Coyle & Schieman, 2007).
Purpose of DNA Fingerprinting
Lach & Patsis (2006) explain that one of the first accepted uses of DNA fingerprinting was in the investigation of sexual assault and rape cases. The criminal investigators must be able to match the DNA of the semen found at the scene of the crime, together with the DNA of the probable suspect to determine who committed the crime. The DNA sample from the rapist is collected using a simple vaginal swab from the victim or any other semen that was released in the crime scene during the assault of the victim (Lach & Patsis, 2006). In addition, paternity tests can be done by applying the DNA fingerprinting process which has been accepted worldwide. It is through the paternity tests that the potential fathers of the child will ask the forensic experts to analyze their DNA samples that will be compared the child and mother’s DNA. The result will prove who among the potential fathers has the most DNA in common with the child in question. (Lach & Patsis, 2006).
In every crime scene, the most common evidence gathered by criminal investigators are fingerprints. The DNA fingerprinting process is a scientific tool to profile the criminal who authored the crime. Sheldon (2011) stated that the fingerprints are reproduced images of the ridged surfaces on the skin, which is an outcome of the oil that has been transferred from the skin. The fingerprints will now be transferred and imprinted on the surface of an object that had been touched by a specific individual. The impression on the surface is usually visible. However, there are instances when the fingerprints are latent or cannot be seen by the naked eye. There are several methods or techniques to collect fingerprints. In fact, the quality of the impression that may be obtained is dependent on the type of technique that is used to preserve and enhance the fingerprint obtained from the crime scene (Sheldon, 2011).
Conclusion
Rosen & Gothard (2009) state that chemistry is an essential tool and plays a critical role during criminal investigations to help solve crimes. The DNA fingerprinting process has been instrumental in profiling of criminals to assess the evidence obtained in a crime scene to arrest the offenders. It is strongly believed that DNA fingerprinting methods have been tried and tested to ensure accuracy. Dempsey & Forst (2011) argue that the use of the revolutionary technological advancements can be useful instruments to promote international law and prevent transnational crimes, organized crimes, and terrorism attacks.
However, it bears to stress that DNA contamination is one of the greatest risks that the evidence must be safeguarded from. In case the DNA sample of evidence is found to be contaminated, it cannot be admitted as evidence inside the courtroom due to inaccuracy of the results obtained. The evidence can be contaminated in the crime scene based on the way it is packaged and transported to the laboratory, and also during analysis (Lach & Patsis, 2006). Hence, these human errors have to be prevented to avoid the inadmissibility of inaccurate evidence.
Finally, fingerprints represent the highest standard of forensic science that has to be handled with utmost caution and care. DNA fingerprinting is a vital tool that will help solve crimes, but must continuously include other novel scientific processes to ensure it is precise and accurate. The poor forensic analysis done by examiners can cause the conviction of innocent people who will be sentenced to suffer life imprisonment for crimes they did not commit. Hence, the reliability of fingerprint evidence can still be developed over time, after application of technology and continuously evolving scientific processes. With the help of chemicals such as luminol, the forensic expert will be able to collect evidence in the crime scenes. This is a breakthrough from the first analysis which appeared to produce no physical evidence, but has been further examined on the particle level to make it impossible to leave a crime without a trace (Lach & Patsis, 2006). Even though there are still some factors that make it difficult to preserve a good DNA sample, it is believed that progress shall develop in the field of forensic science to ensure a limitless future with the advancement of technology in the coming years.
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