Forensic Science Review最新文献

Forensic DNA analysis using short tandem repeats (STRs) has become the cornerstone for human identification, kinship analysis, paternity testing, and other applications. However, it is a lengthy, laborious process that requires specialized training and numerous instruments, and it is one of the factors that has contributed to the formation and expansion of a casework backlog in the United States of samples awaiting DNA processing. Although robotic platforms and advances in instrumentation have improved the throughput of samples, there still exists a significant potential to enhance sample-processing capabilities. The application of microfluidic technology to STR analysis for human identification offers numerous advantages, such as a completely closed system, reduced sample and reagent consumption, and portability, as well as the potential to reduce the processing time required for biological samples to less than 2 h. Development of microfluidic platforms not only for forensic use, but clinical and diagnostic use as well, has exponentially increased since the early 1990s. For a microfluidic system to be generally accepted in forensic laboratories, there are several factors that must be taken into consideration and the data generated with these systems must meet or exceed the same guidelines and standards that are applicable for the conventional methods. This review covers the current state of forensic microfluidic platforms starting with microchips for the individual DNA-processing steps of extraction, amplification, and electrophoresis. For fully integrated devices, challenges that come with microfluidic platforms are covered, including circumventing issues with surface chemistry, monitoring flow control, and proper allele calling. Finally, implementation and future implications of a microfluidic rapid DNA system are discussed.

Capillary electrophoresis (CE) is a versatile and widely used analysis platform with application in diverse areas such as analytical chemistry, chiral separations, clinical, forensics, molecular biology, natural products, organic chemistry, and the pharmaceutical industry. Forensic applications of CE include fragment analysis, DNA sequencing, SNP typing, and analysis of gunshot residues, explosive residues, and drugs. Fragment analysis is a widely used method for short tandem repeat (STR) profiling for human identification (HID) due to the single-base resolution capability of CE. This approach circumvents the tedious and expensive approach of DNA sequencing for STR typing. The high sizing precision, ability to detect fluorescence emitted from multiple dyes, automated electrophoretic runs, and data collection software are key factors in the worldwide adoption of CE as the preferred platform for forensic DNA analysis. The most common CE systems used in forensic DNA analysis include the ABI PRISM® 310, 3100, 3100 Avant, 3130, 3130xl, 3500, and 3500xL Genetic Analyzers (GAs). The 3500 series GAs are developed with features useful for forensic scientists, including a normalization feature for analysis of the data designed to reduce the variation in peak height from instrument to instrument and injection to injection. Other hardware and software features include improved temperature control, radio frequency identification (RFID) tags for monitoring instrument consumables, HID-focused software features, and security and maintenance.

Short tandem repeat (STR) analysis has been the standard in forensic DNA examinations for almost 15 years. The purpose of this article is to provide some perspective on the biological nature of STR alleles themselves, examine underlying distributions of alleles in the STR loci that are routinely used, and to discuss features of these alleles that are not observable with the currently employed methods. Many of the internationally standardized STR loci contain variations of their interrupted repeat structures, either due to the compound or complex nature of the locus or due to nucleotide variations within the simple repeat motif, which inevitably leads them to become more stratified at the population level. Current STR typing procedures utilizing PCR amplification followed by fragment analysis via capillary or gel electrophoresis does not provide the resolution to discern these polymorphisms. Thus, current designation of alleles is operationally and not biologically defined. Although in the comparison of an evidentiary STR profile to that of a potential contributor, the biological nature of the allele may not be of consequence. When comparisons require assumptions of relatedness between individuals, the biological nature of shared alleles becomes an underlying focus. Herein we will discuss the nature of these additional allelic polymorphisms, what is known of their distribution among the STR loci utilized in forensic testing and within populations, and the advantages this level of allelic discrimination has in forensic and relationship testing.

Short tandem repeats (STRs) are regions of tandemly repeated DNA segments found throughout the human genome that vary in length (through insertion, deletion, or mutation) with a core repeated DNA sequence. Forensic laboratories commonly use tetranucleotide repeats, containing a four base pair (4-bp) repeat structure such as GATA. In 1997, the Federal Bureau of Investigation (FBI) Laboratory selected 13 STR loci that form the backbone of the U.S. national DNA database. Building on the European expansion in 2009, the FBI announced plans in April 2011 to expand the U.S. core loci to as many as 20 STRs to enable more global DNA data sharing. Commercial STR kits enable consistency in marker use and allele nomenclature between laboratories and help improve quality control. The STRBase website, maintained by the U.S. National Institute of Standards and Technology (NIST), contains helpful information on STR markers used in human identity testing.

The potential applications of short binary markers to forensic analysis are reviewed. Short binary markers are the most common human genomic variation and include single nucleotide polymorphisms (SNPs) and insertion/deletion polymorphisms (Indels). This review outlines their use and performance in typing highly degraded DNA - the original rationale for developing SNPs for forensic analysis - as well as their ability to infer the ancestry or likely pigmentation characteristics of an individual not present on a national DNA database, thus potentially providing investigative leads. Throughout the review, reference is made to short Indels as a new and potentially powerful alternative to SNPs for enhancing short tandem repeat (STR) results by using a simple amplification to capillary electrophoresis (PCR-to-CE) technique that retains the direct relationship between input DNA and signal strength, offering much improved mixture-detection capabilities while retaining the favorable characteristics of short amplicon PCR.