Encoded evidence: DNA in forensic analysis

Sherlock Holmes said "it has long been an axiom of mine that the little things are infinitely the most important", but never imagined that such a little thing, the DNA molecule, could become perhaps the most powerful single tool in the multifaceted fight against crime. Twenty years after the development of DNA fingerprinting, forensic DNA analysis is key to the conviction or exoneration of suspects and the identification of victims of crimes, accidents and disasters, driving the development of innovative methods in molecular genetics, statistics and the use of massive intelligence databases.     

Subjective interpretation,laboratory error and the value of forensic DNA evidence: Three case studies

This article discusses two factors that may profoundly affect the value of DNA evidence for proving that two samples have a common source: uncertainty about the interpretation of test results and the possibility of laboratory error. Three case studies are presented to illustrate the importance of the analyst's subjective judgments in interpreting some RFLP-based forensic DNA tests. In each case, the likelihood ratio describing the value of DNA evidence is shown to be dramatically reduced by uncertainty about the scoring of bands and the possibility of laboratory error. The article concludes that statistical estimates of the frequency of matching genotypes can be a misleading index of the value of DNA evidence, and that more adequate indices are needed. It also argues that forensic laboratoires should comply with the National Research Council's recommendation that forensic test results be scored in a blind or objective manner.Editor's commentsThe author treats the timely and important issue of laboratory error. Readers will need to read the paper by Lempert in this volume for an alternative interpretation of the 1989 proficiency testing of Cellmark diagnostics.     

Renegotiating forensic cultures: Between law,science and criminal justice

This article challenges stereotypical conceptions of Law and Science as cultural opposites, arguing that English criminal trial practice is fundamentally congruent with modern science’s basic epistemological assumptions, values and methods of inquiry. Although practical tensions undeniably exist, they are explicable—and may be neutralised—by paying closer attention to criminal adjudication’s normative ideals and their institutional expression in familiar aspects of common law trial procedure, including evidentiary rules of admissibility, trial by jury, adversarial fact-finding, cross-examination and the ethical duties of expert witnesses. Effective partnerships between lawyers and forensic scientists are indispensable for integrating scientific evidence into criminal proceedings, and must be renegotiated between individual practitioners on an on-going basis. Fruitful interdisciplinary collaboration between scholars with a shared interest in forensic science should dispense with reductive cultural stereotypes of Science and Law.     

Big forensic data reduction: digital forensic images and electronic evidence

An issue that continues to impact digital forensics is the increasing volume of data and the growing number of devices. One proposed method to deal with the problem of “big digital forensic data”: the volume, variety, and velocity of digital forensic data, is to reduce the volume of data at either the collection stage or the processing stage. We have developed a novel approach which significantly improves on current practice, and in this paper we outline our data volume reduction process which focuses on imaging a selection of key files and data such as: registry, documents, spreadsheets, email, internet history, communications, logs, pictures, videos, and other relevant file types. When applied to test cases, a hundredfold reduction of original media volume was observed. When applied to real world cases of an Australian Law Enforcement Agency, the data volume further reduced to a small percentage of the original media volume, whilst retaining key evidential files and data. The reduction process was applied to a range of real world cases reviewed by experienced investigators and detectives and highlighted that evidential data was present in the data reduced forensic subset files. A data reduction approach is applicable in a range of areas, including: digital forensic triage, analysis, review, intelligence analysis, presentation, and archiving. In addition, the data reduction process outlined can be applied using common digital forensic hardware and software solutions available in appropriately equipped digital forensic labs without requiring additional purchase of software or hardware. The process can be applied to a wide variety of cases, such as terrorism and organised crime investigations, and the proposed data reduction process is intended to provide a capability to rapidly process data and gain an understanding of the information and/or locate key evidence or intelligence in a timely manner.     

The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction

The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.     

Fungal genomics: forensic evidence of sexual activity

The genome sequence of the 'asexual' human pathogenic fungus Aspergillus fumigatus suggests it has the capability to undergo mating and meiosis. That this organism engages in clandestine sexual activity is also suggested by observations of two equally distributed complementary mating types in nature, the expression of mating type genes and evidence of recent genome recombination events.     

The legal status of Russian HIV-infected persons

According to the data, presented by the author and based on the study of opinions expressed by HIV-infected persons, 80% of them are subjected to discrimination. The article deals with the problem of the legal protection of HIV-infected persons in the Russian Federation. Additions and changes in the current legislation regarding foreign citizens and persons in places of confinement are proposed.     

DNA profiling: Social, legal, or biological parentage

DNA profiling in forensic casework is based on comparison of the results of biological evidence with direct reference samples of the individual concerned or with indirect references of his close blood relatives. The selection of reference samples for analysis is crucial to the success of a case; it not only depends on the authenticity of the reference samples, but also on the authenticity of the biological relation of the donors with the person in question. There are situations when the social or legal relationship is not the biological one and there is a need to educate investigating officers, forensic analysts, and the judiciary about the associated problems.     

The exceptional mitochondrial DNA system of the mussel family Mytilidae

Species of the families Mytilidae (sea mussels) and Unionidae (fresh water mussels) contain two types of mitochondrial DNA (mtDNA), the F that behaves as the standard animal mtDNA and the M that is transmitted through the sperm and establishes itself only in the male gonad. The two molecules have, therefore, separate transmission routes, one through the female and the other through the male lineage. The system has been named doubly uniparental inheritance (DUI). Another important feature of sea mussels is that the sex ratio among offspring of a pair mating is determined by the female parent only. The mechanism of DUI remains unknown. One hypothesis that is consistent with all observations is that the standard maternal inheritance was modified in mussels via the evolution of a suppressor gene that is expressed during oogenesis and has two alleles, the inactive and the active allele. In the presence of the active allele in the mother's genotype the egg is supplied with a substance that interferes and the normal mechanism of elimination of sperm mitochondria. This will explain why half of mussels have the father's mtDNA and half do not, but would not explain why presence/absence of paternal mtDNA is linked with the male and female gender, respectively. To provide an explanation for this linkage, one would have to assume that there is a causal relationship between retention of paternal mtDNA and sex determination.     

The CD45 locus in cattle: allelic polymorphism and evidence for exceptional positive natural selection

Cattle in Africa are a genetically diverse population that has resulted from successive introduction of Asian Bos indicus and European B. taurus cattle. However, analysis of mitochondrial genetic diversity in African cattle identified three lineages, one associated with Asian B. indicus, one with European B. taurus, and a third ascribed to an indigenous African sub-species of cattle. Due to their extended coevolution, indigenous African herbivores are generally tolerant to endemic African pathogens. We are interested in identifying alleles derived from the indigenous African cattle that may be associated with tolerance to African pathogens. An analysis of the locus which encodes the abundant plasma membrane-associated tyrosine phosphatase, CD45, identified three highly divergent allelic families in Kenya Boran cattle. Analysis of allelic distribution in a diverse range of cattle populations suggests a European B. taurus, an Asian B. indicus, and an African origin. This demonstrates not only significant allelic polymorphism at the CD45 locus in cattle but also convincing autosomal evidence for a distinct African sub-species of cattle. Furthermore, maximum-likelihood analysis of selection pressures revealed that the CD45 locus is subject to exceptionally strong natural selection which we suggest may be pathogen driven.     

'Wonderment and dread': representations of DNA in ethical disputes about forensic DNA databases

The national DNA Database of England & Wales is the largest forensic DNA database in the world. Since 1995 it has quickly developed to hold the genetic profiles of over two million people. This collection of tissue samples, taken without consent from a sizeable collection of the population, has engendered a number of ethical commentaries on its legitimacy as a proportionate response to crime. This paper examines the ways in which the ethical discourses, which surround the uses of the National DNA Database, drew upon and deployed a number of distinct representations of DNA. It is argued that key ideas about DNA have become central to everyday assertions about the benefits and dangers of this forensic technology.     

cDNA cloning, recombinant expression and characterization of polypetides with exceptional DNA affinity.

Polypeptides remaining tightly associated with isolated genomic DNA are of interest with respect to their potential involvement in the topological organization and/or function of genomic DNA. Such residual DNA-polypeptide complexes were used for raising monoclonal antibodies by in vitro immunization. Screening of a murine lambdagt11 cDNA library with these antibodies released a positive cDNA (MC1D) encoding a 16 kDa polypeptide. The cloned homologous human cDNA (HC1D) was identified in the dbest data base by partial sequence comparison, and it was sequenced full length. The cDNA-derived amino acid sequences comprise nuclear location signals but none of the known DNA-binding motifs. However, the recombinantly expressed proteins show in vitro DNA binding affinities. A polyclonal antiserum to the recombinant MC1D protein immunostains sub-nuclear structures, and it detects a residual 16 kDa polypeptide on western blots of DNA digests. These results support the conclusion that the cloned cDNAs reflect mRNAs encoding one of the chemically-resistant polypeptides which can be detected in isolated genomic DNA by sensitive techniques, e.g. by125Iodine labeling and SDS-PAGE.     

The forensic debut of the NRC's DNA report: Population structure,ceiling frequencies and the need for numbers

This paper reviews judicial opinions that have discussed the April 1992 recommendations of a committee of the U.S. National Research Council concerning the statistics of forensic DNA profiles obtained with single-locus VNTR probes. It observes that a few courts have held ceiling frequencies (as opposed to less conservative estimates) admissible, but that the implications of the scientific criticisms of the ceiling procedures have yet to be addressed adequately in court opinions. It urges courts to distinguish between policy judgments and scientific assessments in both the NRC report and the scientific literature, and to defer less to the former than to the latter.Editor's commentsScientists caught up in the debate over the use of DNA for human identification may not be fully aware of the legal consequences of their pronouncements. The author provides a very useful discussion of these consequences in showing how courts have interpreted the 1992 NRC report.