Deoxyribonucleic Acid Profiling in Forensics Research Paper

Abstract

This paper explores the effectiveness of DNA profiling in forensics. It looks at the history of DNA profiling focusing on three stages of its development: multilocus probing (MLP), single locus probes (SLP), and short tandem repeat (STR). The paper examines STR analysis, the use of polymerase chain reaction (PCR), and the second-generation multiplex (SGM) system. The effectiveness of trace DNA profiling and familial searching systems is also discussed in the paper. The last part of the analysis includes discussion of the potential for error in DNA profiling.

Introduction

The first DNA case was processed by a geneticist from the University of Leicester, Britain, Sir Alec Jeffreys, in 1984 (Aronson, 2011). After the debut of DNA profiling in the British legal system in 1985, the method quickly spread to the U.S. where it was adopted by two giant biotechnology corporations—Lifecodes Corporations and Cellmark Diagnostics (Aronson, 2011). During the decades that followed, forensic DNA profiling has been a subject of intense scrutiny and debate by scientists and policymakers. The enormous impact of forensic genetics on legal process raised significant controversy in the media that were questioning its validity. Fortunately, much progress has been made since the introduction of DNA evidence: both methods for evaluating standard DNA profiles and the understanding of the technology by the legal system have improved (Balding & Steele, 2015). Now, it is considered “the gold standard of forensic analysis” (Jamieson & Bader, 2016, p. 3). It has to do with the fact that DNA is a material that fulfills most of the criteria making “the perfect forensic technology to establish a person’s presence at a scene of crime” (Jamieson & Bader, 2016, p. 3). DNA is unique, does not change over time, and, most importantly, it is usually found in quantities that allow establishing a match. This paper aims to explore the effectiveness of DNA profiling in forensics. It will focus on short tandem repeat (STR) as the last stage of its development and examine the use of trace DNA profiling as well as familial searching systems. The paper will also discuss the potential for error in DNA profiling.

History of DNA Profiling

The modern method of profiling DNA is based on two independent discoveries in molecular biology that happened almost at the same time. American scientist, working for Cetus Corporation made a breakthrough that allowed to develop the polymerase chain reaction (PCR) in 1984 (Jamieson & Bader, 2016). At the same time, a British biologist, Sir Alec Jeffreys, explored “the individual-specific banding patterns after restriction fragment-length polymorphism (RFLP) analysis of repeated DNA sequences” (Jamieson & Bader, 2016, p. 9). The earliest version of the method was dubbed as DNA fingerprinting by its developers and relied on the restriction of 0.5–10 μg of extracted DNA material with the help of enzyme HinFI that was “followed by Southern blotting hybridization with probes termed 33.5, 33.6, 33.15, designed to bind to multiple ‘minisatellites’ present in the restricted DNA” (Jamieson & Bader, 2016, p. 9). This technique of DNA profiling is known as multilocus probing (MLP) method.

It allowed binding probes to several fragments of DNA simultaneously and resulted in ‘barcode’ pattern that is often associated with DNA profiling. Autoradiogram image allows measuring differences between repeating patterns of probe sequences in DNA fragments. Jeffery et al. established the Mendelian inheritance of probes by conducting a pedigree analysis study exploring the banding pattern in 54 related and 20 unrelated individuals (Jamieson & Bader, 2016). The findings of the study suggest that the probability of two unrelated persons having identical DNA patterns for 33.15 probes alone equals 3 × 10^-11 (Jamieson & Bader, 2016). Due to the complexity of the process of interpretation of MLP images, single locus probes (SLP) have been adopted for the use with variable numbers of tandem repeat (VNTR) as markers in modern DNA profiling (Jamieson & Bader, 2016).

The potential of Jefferys’ discovery for the use in a criminal investigation has opened the necessity for further statistical validation of the method. Early studies analyzing “population frequencies and application to casework samples” using MLP 33.15 have revealed that the method of DNA profiling has significant limitations (Jamieson & Bader, 2016, p. 9). For example, vaginal swabs that were stored for four years produced only 62 % success rate for MLP fingerprinting (Jamieson & Bader, 2016). Similar SLP studies have shown that there are significant variations in gel images interpretations produced by different European laboratories (Jamieson & Bader, 2016). The significant breakthrough in DNA fingerprinting allowing to overcome these limitations occurred in the early 1990s when Weber et al. discovered an alternative type of DNA markers—short tandem repeat (STR) (Jamieson & Bader, 2016).

STR Analysis

STR analysis is the third state in the evolution of DNA profiling technology. The method involves “the use of polymerase chain reaction (PCR) of STR loci” (Buckleton, Triggs, & Walsh, 2016, p. 3) by linking it to a molecular photocopier that could amplify infinitely small amounts of DNA. Unlike MLP and SLP that required 500 ng of DNA fragments for analysis, PCR could be effectively used with less than 1ng. PCR reaction uses smaller alleles averaging between 100 and 400 bp that differ by only one repeat; therefore, it is more efficient with fragments of low weight (Buckleton et al., 2016). PCR reaction in STR is run at 27-34 cycles each of which could almost double the amount of DNA resulting in amplification by a factor of 134 million to 17 billion (Buckleton et al., 2016). It should be noted that perfect amplification is yet to be achieved. However, optimization efforts have allowed reducing “the amount of template required for the generation of full DNA profile to just 500 pg (Jamieson & Bader, 2016, p. 11) and making possible to produce partial profile from a PCR product length that equals to 50 pg. The development of PCR-based STR analysis has allowed to significantly increase the sensitivity of the DNA profiling, reduce its time to less than 24 hours, and improve the cost-effectiveness of the analysis (Buckleton et al., 2016). It has also made possible to analyze degraded DNA material that is very common in forensics. Moreover, PCR-based STR analysis has rendered DNA profiling to automation. It should be mentioned that even though it is possible to run the analysis of DNA samples in less than 24 hours, an average turnaround time equals to five days due to the substantial amount of paperwork that has to be filled (Buckleton et al., 2016).

The last generation of STR system of forensic DNA analysis is called second-generation multiplex (SGM) system and its application for filling the national criminal intelligence DNA database (NDNAD) started as early as in 1995 (Jamieson & Bader, 2016). The system could be used to detect and resolve DNA profiles that are mixed at ratios between 1:10 and 10:1 with “a probability of chance association calculated as 1 × 10^-8 (Jamieson & Bader, 2016, p. 78). In 2000, American division of Perkin Elmer called Applied Biosystems (ABI) modified SGM and produced The AmpFlSTR® SGM Plus™ system with a probability of a chance association significantly exceeding that of standard SGM (Jamieson & Bader, 2016, p. 78). According to Jamieson and Bader (2016), the new system is so precise that its match probability equals to one in a billion for unrelated persons and one in a million for individuals having parent/child relations. Conservative estimate of a chance association for siblings is 1 in 10,000 (Jamieson & Bader, 2016). Modified system has significantly increased the effectiveness of DNA profiling while remaining back compatible with data stored in NDNAD.

The effectiveness of Trace DNA Profiling

Recovery of DNA material that is not present as a stain is generally referred to as trace recovery and evidence left at the crime scene through either direct disposition such as touching, spitting, or coughing among others or indirect disposition via contact with a surface is called trace DNA (Bond & Weart, 2016). The quantity of recovered material is directly related to an absorbent substrate in which it has been deposited and the contact time. It should be noted that quantity of indirectly deposited material varies depending on “an individual’s ability to shed sebaceous fluid on the skin surface” (Bond & Weart, 2016, p. 11). Moreover, numerous studies suggest that effectiveness of material extraction could be affected by choice of swabs. The effectiveness of trace DNA for profiling in forensics was examined in recent studies in New Zealand and Australia that proved that up to 20% of trace DNA could be recovered from handled surfaces (Bond & Weart, 2016). The findings of a study comparing the effectiveness of recovering, profiling, and searching trace DNA by U.K. and U.S. police forces suggest that there is no “statistically significant difference between the number of useful profiles obtained from either single or multiple recoveries for any evidence category” (Bond & Weart, 2016, p. 17).

It should be mentioned that modern techniques of trace DNA profiling have changed case acceptance policies in the U.S. to include items that have been left by a person of interest or have been contacted by them for an extended period and might contain cellular material. Bond and Weart (2016) argue that development of “techniques utilizing smaller amplicon sizes through single nucleotide polymorphisms (SNPs) in next-generation sequencing kits” (p.17) will allow to significantly improve the effectiveness of DNA profiling.

Familial Searching

Familial searching is a powerful service that has been used in the forensic community for more than a decade. The tool was introduced in 2002 by Forensic Science Service Ltd. (FSS) and could be considered a testament to the effectiveness of DNA profiling in forensics. It allows using full DNA profiles that were deposed on a crime scene “by the true offender, but where no match was recorded with the profiles of any individuals retained on the NDNAD” (Maguire, McCallum, Storey, & Whitake, 2014, p. 1) for the promotion of criminal investigations. Familial searching relies on the supposition that a lack of an offender’s profile in NDNAD means that it is either their first offense or previous offenses have not been detected. Familial search algorithms help to identify an offender’s relatives of the first order or other close genetic relatives whose profiles are present in NDNAD. A recent report from the National Bureau of Statistics suggests that 50% of incarcerated prisoners that are reporting having minor children also had the first order relatives who have been convicted at some point in their lives (as cited in Maguire et al., 2014). The DNA familial program conducted in England and Wales corroborated the findings of the report. The effectiveness of this DNA profiling method is confirmed by the fact that it has been successfully used to identify offenders in 210 cases in the U.K. (Maguire et al., 2014). Moreover, the application of familial searching as an investigative tool in the U.S. that was introduced in 2008 proved that the method could be used to “rapidly locate potential relatives of a perpetrator” (Maguire et al., 2014, p. 8). Therefore, it could be argued that if used in accordance with principles of non-maleficence, this method of DNA profiling could be extremely effective in supporting the Criminal Justice System.

The Potential for Error in DNA Profiling

The reliability of forensic DNA profiling has been touted by numerous scholar articles and courtroom testimonies since the start of its use in 1987 (Thompson, n.d.). The validity of the method has been recognized by the National Research Council that stated that it should not be doubted (Thompson, n.d.). However, it should be noted that even though various alterations that have been introduced to the PCR method over the last decades has led to the significant improvement of its efficiency, numerous factors might contribute to the error occurrence in data produced by the technique. It has to do with the fact that DNA polymerases that are being used in the PCR method could produce inaccuracies during amplification. Mispriming could also potentially contribute to the creation of unexpected variability in the success rate of the technique (The Forensics Library, n.d.). Moreover, due to the fact that partial profiles contain fewer alleles, there is a higher probability of a chance match for them. Nonetheless, there is ample evidence suggesting that using DNA for identifying offenders leads to better administration of justice and reduces recidivism rates thereby resulting in significant social cost savings (DOJ, n.d.). Therefore, it could be argued that DNA profiling is an effective forensic method that can improve accuracy in the system of criminal justice.

Conclusion

The paper examined the history of DNA profiling and explored STR analysis and the potential for error posed by this method. The significant breakthrough in DNA fingerprinting that occurred during the last decades helped to change legal process to a significant degree. Moreover, the media exposure of DNA profiling has helped to improve both methods for evaluating standard and partial DNA profiles as well as the understanding of the technology by the legal system. Even though systems like AmpFlSTR® SGM Plus™ are so precise that their match probability equals to one in a billion for unrelated persons and one in a million for individuals having parent/child relations, there is still a potential for errors that could occur due to the inaccuracies during amplification process or because of mispriming. However, there is ample evidence suggesting that using DNA profiling is an effective forensic instrument that leads to better administration of justice and reduces recidivism rates thereby resulting in significant social cost savings.

References

Aronson, J. (2011). Genetic witness. Saint John, Canada: Rutgers University Press.

Balding, D., & Steele, C. (2015). Weight of evidence for forensic DNA profiles (2nd ed.). Hoboken, NJ: John Wiley & Sons.

Bond, J., & Weart, J. (2016). The effectiveness of trace DNA profiling-a comparison between a U.S. and a U.K. law enforcement jurisdictions. Journal of Forensic Sciences, 34(7), 11-18.

Buckleton, J., Triggs, C., & Walsh, S. (2016). Forensic DNA evidence interpretation (2nd ed.). Boca Raton, FL: CRC Press.

DOJ. (n.d.). Using DNA to solve crimes.Web.

Jamieson, A., & Bader, S. (2016). A guide to forensic DNA profiling. Glasgow, England: Wiley.

Maguire, C., McCallum, L., Storey, C., & Whitaker, J. (2014). Familial searching: a specialist forensic DNA profiling service utilizing the National DNA Database® to identify unknown offenders via their relatives—The UK experience. Forensic Science International: Genetics, 8(1), 1-9.

The Forensics Library. (n.d.). DNA analysis. Web.

Thompson, W. (n.d.). The potential for error in forensic DNA testing. Web.