Combined DNA Index System (CODIS) is a brainchild of the FBI which blends technologies in DNA and computers for effective comparison of DNA profiles. The CODIS system has two indices which are used to produce leads for investigation after biological evidence is recovered following a crime. Convicted offender index has DNA profiles of violent criminals like murderers and rapists. Individuals convicted of violent crimes have their DNA extracted, and the profile remains with tis consequently stored in the CODIS database. The database also supports population DNA profiles. The second batch of DNA profiles comprise all the DNA pieces of evidence that were obtained from the crime scene, active and passive. After collection of DNA evidence from the crime scene, they are taken to the lab and processed and later fed to the CODIS database. CODIS then runs the profile, with the help of computer software, against the database to find a match. The matches made can link crimes such that serial offenders can be determined. Matches can give the police a directed insight which can help them to investigate the crime thoroughly. CODIS works on three levels comprising of the local (county) database, the state database, and the federal database. Local databases are used locally and every offender index added is forwarded to the higher level. Forensic laboratories within each jurisdiction can share information and comparison of their profiles are done before they are used.
In 1981 Patricia Beard was strangled to death inside her studio apartment. Beard had a mental disorder at the time, and her family did not know where she was for a few days until her body was discovered partly clothed (Michael, 2016). Post-mortem crime scene kit offered DNA evidence in July 2011, and the authorities entered it into the CODIS database. Two years later in 2013, the system hit a match which resulted in the arrest and charge of Hector Bencomo Hinojos a man from Pennsylvania, 53 years of age. The man denied ever knowing Beard or being in the area at the time, but the DNA evidence not only placed him at the scene but also indicated involved himself in sexual contact with her just moments before her death. Evidence from his wife shed light on his character as a violent man, and he was consequently found guilty of first-degree murder of Patricia Beard (Alexander, 2017, 4).
William Gregory was exonerated after almost a decade in prison for a crime he did not commit. Gregory had been arrested and charged in a court of law for attempting to rape a victim in his apartment and was sentenced on identification be the victim in a police parade where suspects were lined up (Alexander, 2017, 4 ;Ballantyne et al., 2014, 1031). The only tangible evidence that was available in the courtroom was hair. The six head hairs were obtained from pantyhose which was taken from the victim's home by the suspect to use as a mask. At his trial in 1993 a forensic hair expert, microscopist examined the hair and testified that they could have been Gregory's. This evidence and the backing testimony from expert opinion formed the backbone of the case against Gregory and was heavily relied upon for his conviction (Alexander, 2017, 4). Lucky for him; however, the hairs were preserved, and once the mDNA technology came to place, they decided to reexamine the strand in 2000. Analysis of the hairs determined that although they shared similar mitochondrial DNA profile, the hair indeed had a different profile to that of the accused, William Gregory. In addition, the analysis concluded that the hairs did not belong to the victim either. Gregory was released from prison shortly after the emergence of the new evidence, and he became the first case in U.S where mitochondrial DNA played a vital role in exoneration of a victim. The case, however, remains unresolved (Alexander, 2017, 4).
Nuclear DNA is popularly used in the identification of individuals against the CODIS database. However, in the late 1990s application of mDNA in forensics was introduced (Li, 2015). Although at first it was used for human skeletal remains so that family members can identify their own for burial. In such cases, nuclear DNA is usually degraded and not sufficient for identification (Melton, 2011). Whereas only two copies nuclear DNA is present in a cell, thousands of mDNA are present in each cell making it a resourceful reservoir for DNA. The mDNA is unique in a population such that only maternal family members have similar copies. Like in the case of William Gregory, mDNA evidence can be a powerful tool in the courtroom able to determine the decision taken by the bench on whether an individual is guilty or not (Melton, 2011). There is therefore increased application of the method in legal cases especially in the identification of DNA from hair. However, the use of microscopy in characterizing hair is still a viable method only that it should be used in conjunction with mDNA (Parson et al., 2015, 12).
In 1992, two women e were discovered dumped Phoenix. One of the women was young, and her body was disposed of in the Arizona Canal. The next one was found in the same place ten months later (Houck & Siegel, 2009). The police had no clue as to who was committing all that crime (Alexander, 2017, 4). The case, therefore, went cold. It wasn't until thirteen years later, in 2015, that an actionable lead emerged through a genealogical forensic expert, Colleen Fitzpatrick. She cross-referenced the DNA in the custody of the police against the public databases (Purps et al., 2014, 18). There is a growing number of databases mostly by genealogical minded individuals who forward their profiles in the hope of finding their distant relatives. Since it was known that the suspect was a man, she used the Y-STR testing to search the database only along the Y-DNA line to determine whether she could obtain the profile of the suspect involved in the murder of the two women 13 years earlier (Michael, 2016; Baker et al., 2001, 127). Fortunately for Fitzpatrick and the family members of the victims, the databases returned a positive match two weeks later. The forensic genealogist was able to identify an individual with the surname Miller as the possible suspect. After analysis of their records from the time of the commission of the crime, the law enforcement officers were able to pinpoint Bryan Patrick Miller as the principal suspect from the list they had. Further DNA analysis of Miller in comparison to the one obtained from the victims was also a match. Consequently, Miller was arrested in 2016 and arraigned in court for double homicide and was charged with 1st-degree murder (Alexander, 2017, 4).
Y-STR is specific to male individuals, Y-chromosome and has found broad application in forensics especially when autosomal profiling of DNA fails to give satisfactory information (Buckleston et al., 2016; Ghatak et al., 2013, 224). Application of a gene fragment of the Y-chromosome infers the biological sex of the suspect done. Then haplotypes comprising of Y-STRs characterize the paternity of the suspect. The method is efficient mostly in cases of sexual assault by male suspects. This method can help pin the crime on an individual or can help the police officers by providing an investigative lead which can ultimately lead to the arrest and conviction of the perpetrator of a crime. Considering these trends, the future of Y-STR testing looks bright, and with continuous improvement of methodologies, future use of the method will be seamless and efficient (Kayser, 2017, 624)
Biological Sources of DNA
- White blood cells
- Epithelial cells
Methods Extracting DNA
Bloodstain on a Shirt
The organic extraction method is the most applied in the extraction of DNA from Bloodstains (Jobling & Gill, 2004,739; Butler, 2011; (Klintschar & Neuhuber, 2000,670). The part of the cloth where the stain is located is cut off and dipped into a buffer solution. Blood proteins are broken down by proteinase K, and through Phenol-chloride, liquid aqueous DNA is obtained after the proteins are removed. Chrolo-form then removes any traces of phenol to remain with DNA pellets. Washing the pellets with ethanol leaves behind DNA crystals for further processing to develop a DNA profile. The DNA can be further processed by PCR to develop A DNA profile (Haas et al., 2012, 78).
In the extraction of DNA from postage stamps can be done by use of the Nexttec method. This method is more efficient compared to the silica-based method (Lauk & Schaaf, 2007; Horsman et al., 2007, 785 ). DNA is extracted through Qiagen QIAamp DNA mini kit. The postage stamp is cut into small pieces for ease of absorption. The sample is inserted in a Nexttec buffer and placed in a column with a spacing material. The column is then centrifuged at 16,000g for 3 minutes to make sure the membrane is dried. DNA is eluted in 100 micro-Liter of elution buffer (Vandewoestyne et al, 2013, 317; Castella et al., 2006, 72).
Hair Shaft With No Root
Since hair shaft lacks nucleic DNA, forensic investigation relies on mDNA which is available in relatively large quantities per cell. The mDNA does not depend on the availability of the hair root since it can be obtained from the shaft. However, use of phenol/Chloroform method is used to extract mDNA from the hair shafts (Hofstadler, 2013; Takayanagi et al., 2003, 762). The hair is cut into 5 mm pieces and dipped into sodium hypochlorite for decontamination. After addition of lysis solution and the enzyme, the tube is agitated to ensure the contents are well mixed. The extract obtained after incubation is then digested by phenol/chloroform and consequently centrifuged. The aqueous phase is then separately acquired, and 3M sodium acetate and ethachimate are added. The tube is then mixed gently, and ethanol is added. The solution was then centrifuged and cashed to give pure mDNA. This method is simple and less expensive to use than most other methods (Fraser & Williams, 2013; Graffy & Foran, 2005, 125).
Vaginal Swab Containing Semen
Samples emanating from sexual assault victims such as semen through vaginal swab contains epithelial cells from the victim. It is therefore common to find the more epithelial cells compared to Sperms from the perpetrator (Fraser & Williams, 2013; Setzer & Ballantyne, 2008, 298). There is, therefore, a need to separate the two. Differential lysis of the samples do the separation of epithelial cells from semen in the absence and presence of dithiothreitol (DDT) which results in a generation of an epithelial lysate and a sperm lysate respectively in separate vials. The DNA can, therefore, be extracted by the differential method and developed to create a profile (Lee & Shewale, 2006, 6; Gamba et al., 2016, 461; Rohland & Hofreiter, 2007, 348; Yang et al., 2014, 190).
Alexander, L. (2017). Top 10 Murder Mysteries Finally Solved Using Forensics. Listverse. [online] Available at: https://listverse.com/2017/04/09/top-10-murder-mysteries-finally-solved-using-forensics/ [Accessed 14 Nov. 2018].
Baker, L.E., McCormick, W.F. and Matteson, K.J., 2001. A silica-based mitochondrial DNA extraction method applied to forensic hair shafts and teeth. Journal of Forensic Science, 46(1), pp.127.
Ballantyne, K.N., Ralf, A., Aboukhalid, R., Achakzai, N.M., Anjos, M.J., Ayub, Q., Balazic, J., Ballantyne, J., Ballard, D.J., Berger, B. and Bobillo, C., 2014. Toward Male Individualization with Rapidly Mutating YChromosomal Short Tandem Repeats. Human mutation, 35(8), pp.1031.
Buckleton, J.S., Bright, J.A. and Taylor, D. eds., 2016. Forensic DNA evidence interpretation. CRC press. Gamba, C., Hanghoj, K., Gaunitz, C., Alfarhan, A.H., Alquraishi, S.A., AlRasheid, K...
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