DNA profiling is a criminal investigation techniques employed by forensic experts. It is, however, also useful for other purposes such as parentage determination among others. DNA profiling requires that a sample is present, because it involves comparison of different DNA samples to determine their similarities or differences and reach a conclusion. A buccal swab is the most common way of DNA reference sample collection (Butler, 2009 ) . It involves swabbing the inside of a person’s cheek and extracting DNA sequences from the cells obtained thereof. However, in case it is not possible to use this method, as often is in criminal investigations, reference DNA can be obtained from various other sources such as body fluids (Butler, 2009 ) . They include semen, blood, vaginal lubrication, or other tissue that may be obtained from personal items such as toothbrushes. Reference DNA may also be obtained from previously stores samples such as biopsies. The reference DNA is the DNA sample against which other DNA will be compared.
DNA profiling involves a number of steps, the first of which is DNA extraction from the source sample such as saliva or sperm. Extraction is the separation of the DNA material from the cell, whereby the rest of the cellular components are discarded. Some of the methods used in doing this include Chelex, organic and solid phase extraction (Butler, 2009 ) . Upon extraction, there are various forms of DNA analysis. Restriction fragment length polymorphism (RFLP) analysis was one of the methods that were previously used. It is, nevertheless, not viable if the DNA available is degraded or is in limited quantities. Polymerase chain reaction (PCR) analysis replaced RFLP analysis due to better effectiveness. In this method, DNA sequences can be amplified and therefore analyzed easily (Jamieson & Bader, 2016 ) . Short tandem repeats (STR) analysis is a variation of PCR. Amplified fragment length polymorphism is a technique which is cost effective and therefore often used in low income nations.
Delegate your assignment to our experts and they will do the rest.
Degraded DNA is common in many crime scenes given that extended periods of time may elapse before crime scenes are discovered. Degraded DNA is DNA in which the strands have been broken down into smaller components by contact with natural substances such as enzymes or water (Jamieson & Bader, 2016 ) . Mitochondrial analysis is usually a technique used when DNA samples are degraded. PCR techniques such as multiplex PCR are useful in analysis of degraded DNA. MiniSTR analysis is also effective in matching degraded DNA components (Butler, 2009 ) . DNA mixtures, another prevalent challenge in DNA profiling, are samples from multiple contributors. A sample from two of more contributors is difficult to analyze, especially is the contribution from each of the individuals is almost equal.
DNA profiling is used to solve crimes by using DNA samples obtained from crime scenes to identify the persons who were present at the crime scene at the time when the crime was perpetrated. These individuals can then be traced and other methods can be used by investigators to determine their role in the crime, or explain the presence of their DNA at a crime scene. DNA evidence is often conclusive in the conviction or exoneration of suspects in numerous cases such as murder, assault, rape, etc.
Analysis of Case study 2
It is apparent that the man has been free for 10 years after the crime was committed simply because a DNA profile on the suspect has not been done. This underscores the importance of DNA profiling in solving of crimes. According to the case, the man is suspect based on his close relationship with the rape victim and his actions after the rape incidence occurred. It is likely that the man was questioned after the rape incident. However, in cases where the victim is unable to identify the perpetrator, conviction is difficult due to lack of evidence. The problem is amplified in this case due to legal restrictions preventing the use DNA profiling.
Various items may be obtained from the crime scene as part of physical evidence. They include:
Bed sheets/linens
These are important as the carry DNA evidence of the parties involved. The DNA evidence could be obtained from the fluids spilled on the sheets or linens such as sperm, blood or saliva.
Condoms
Condoms are always a source of DNA evidence, from both the perpetrator and the victim. This evidence can be obtained from body fluids found on the condom such as sperm, blood or vaginal fluids.
Weapons
In many cases, a weapon may have been used by the perpetrator to subdue and/or incapacitate the victim, or by the victim in self-defense (Aronson, 2007 ) . The weapon is likely to contain evidence such as hair, skin tissue or blood residue.
Panties/other torn clothing
These clothing may often be found at sexual assault scenes. They are important as they are likely to contain DNA evidence in from body fluids such as vaginal discharges or blood.
Other spilled blood or sperm samples
There are likely to be various blood samples obtained from sexual assault scenes. This is in reference to the blood that could have been spilled on surfaces or floors and therefore needs to be swabbed or scooped. In most cases of sexual assault, there is a struggle as the victim attempts to defend themselves, in which case either or both parties may be hurt drawing blood (Lincoln & Thomson, 1998 ) . Blood samples from the victim may also result from injury caused by the act of forceful sexual penetration or from any injury that may have been inflicted by the perpetrator. The perpetrators blood may have resulted from injuries caused by the victim in her defense.
DNA Tests
Various techniques may be used to test the DNA obtained. First, it has to be extracted from the evidence item. The perpetrator’s DNA may have been obtained through surreptitious DNA collection whereby it is collected without the owner’s knowledge (Aronson, 2007 ) . DNA can be collected from any item whose access is legally permissible such as garbage components. For instance, disposable cups may contain traces of saliva while tissues may contain DNA residue from skin. Moreover, reference DNA may be available in the country’s DNA database, especially if the suspect is a past offender.
DNA testing processes
PCR based genetic fingerprinting is the most reliable genetic test based on its specificity and subjectivity. PCR is also useful even in cases where DNA is fragmented, as is likely in this case (Lincoln & Thomson, 1998 ) . If the perpetrator’s DNA was collected surreptitiously, it is likely to be highly fragmented. This would also be the case if the crime was discovered a considerable amount of time after the crime was committed, or if the crime scene had been tampered with.
Suspect Conviction
The evidence convicted the suspect after his DNA was found to be similar to that from a sample obtained from the crime scene. This evidence was inevitably combined with complimentary evidence, physical of circumstantial, which by itself, had been insufficient to convict the suspect (Lincoln & Thomson, 1998 ) . Moreover, the suspect had exhibited some suspect behaviour such as the immediate relocation after the rape incidence.
References Top of Form
Aronson, J. D. (2007). Genetic Witness: Science, Law, and Controversy in the Making of DNA Profiling . New Brunswick, Rutgers University Press Top of Form
Butler, J. M. (2009). Fundamentals of Forensic DNA Typing . Burlington: Elsevier Science. Bottom of Form
Top of Form Jamieson, A., & Bader, S. (2016). A Guide to Forensic DNA Profiling . Chichester, West Sussex, United Kingdom, Wiley Top of Form
Lincoln, P. J., & Thomson, J. (1998). Forensic DNA profiling protocols . Totowa, N.J: Humana Press.
