2Institute of Investigative Genetics, University of North Texas Health Science Center, Ft. Worth, TX, USA
3Faculty of Health Science and Medicine, Bond University, Gold Coast, Queensland, Australia
Molecular biology tools have enhanced the capability of the forensic scientist to characterize biological evidence to the point where it is feasible to analyze minute samples and achieve high levels of individualization. Even with the forensic DNA field's maturity, there still are a number of areas where improvements can be made. These include: enabling the typing of samples of limited quantity and quality; using genetic information and novel markers to provide investigative leads; enhancing automation with robotics, different chemistries, and better software tools; employing alternate platforms for typing DNA samples; developing integrated microfluidic/microfabrication devices to process DNA samples with higher throughput, faster turnaround times, lower risk of contamination, reduced labor, and less consumption of evidentiary samples; and exploiting high-throughput sequencing, particularly for attribution in microbial forensics cases. Knowlege gaps and new directions have been identified where molecular biology will likely guide the field of forensics. This review aims to provide a roadmap to guide those interested in contributing to the further development of forensic genetics.
Forensic science has embraced the use of DNA molecular biology tools for diagnostic purposes more than any other scientific field. The discipline has been driven by the need for high-resolution human identity testing techniques. Over the past 20–25 years, forensic science has developed and implemented various robust and reliable DNA typing technologies (1,2,3). Successes have enabled the reliable typing of extremely minute quantities of DNA, with a resolving power such that, in many cases, the number of evidence-sample contributors can be reduced to a few individuals, if not just one source. In addition, forensic molecular biology tools are very reliable because of well-defined validation requirements (4,5).
Given the forensic field's maturity, it could be assumed that dramatic changes in technology will not be sought and only refinements will be embraced. There are fewer demands to meet technologically; in fact, the capability to routinely type samples such as a cigarette butt or a single strand of hair has exceeded the expectations of most scientists who first began using molecular biology tools to characterize forensic biological evidence. Rather than using restriction length polymorphism analysis by Southern blot–based hybridization methods (6,7,8), scientists in the field are now routinely using PCR-based methods coupled with automated fluorescent detection technologies (9,10,11,12,13,14,15,16,17). The use of offender and forensic sample DNA databases contributes to reticence for change. These databases were developed to help investigate future crime and have been standardized on a core set of short tandem repeat (STR) or microsatellite loci (18,19). Because of the size of these databases [for example, there are >6 million reference profiles in the United States Combined DNA Index System (CODIS) database (20)], there is a substantial movement to maintain just the current core genetic marker repertoire. Additionally, because of the substantial resource outlay to validate molecular biology analytical systems, to equip a laboratory, and to educate and make proficient practitioners; as well as the efforts undertaken to gain admissibility in the courtroom (21), forensic scientists tend not to change sound methodologies quickly. One might predict, therefore, that there are not likely to be any dramatic changes in the molecular biology tools used in forensic science. Such a view, however, would be myopic because there are several areas where molecular biology could offer improvements to the capabilities of the forensic scientist. Indeed, it is incumbent on the forensic scientist to be vigilant and embrace new technologies that will benefit society by their ability to analyze more challenging samples in an effort to continue to exonerate the innocent, to enhance abilities to solve crime, and to identify missing persons.
With analysis success, there is motivation to attempt to analyze more difficult samples, such as trace samples termed touch DNA or low copy number (LCN) (22,23). DNA databases may not have been exploited fully and could provide leads to new investigative questions. In addition, the recently developed field of microbial forensics will exploit high-resolution, high-throughput technologies beyond those needed for human identification. Therefore, the future of molecular biology in forensic science still promises to be dynamic.
Predicting the future is never exact, and fundamental leap technologies are not obvious. Thirty years ago, few if any would have predicted the PCR method and the impact it has had on molecular biology. In this review, we describe the primary gaps in the handling and analysis of forensic biological evidence that are being or are likely to be filled by molecular biology tools. The gaps are not unreasonable predictions; many are obvious needs that will drive development in the forensic science field for the next 5–10 years. The areas that will be addressed are: (i) improvements to the current limits of typing samples of limited quantity and quality; (ii) investigative information including phenotypic inference from a DNA sample and pharmacogenetic information for molecular autopsy, tissue type determination by expression analysis, and microbial forensics; (iii) microbial forensics; and (iv) automation with a focus on in-field testing.
Because of space limitations, the topics herein are only discussed briefly; readers should refer to the references (and their citations) for more details and other examples beyond those provided here. Hopefully, these gap assessments will help guide those who invest resources in forensic molecular biology diagnostics.