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Modern Forensics: Mitochondria DNA

Introduction

Forensic science which is famous in some parts of the world as officially authorized remedy is a field that seeks to assist adjudicators and judges in solving lawful cases, not only in criminal law but also in civil cases. The subject is vast and has particularly got intersection between limits of biology, physics, chemistry and mathematics, with as diverse as ballistics and botany, and analysis of handwritings, ear prints, and fingerprints and recorded sound. Since eighties one precise biological technique has transfigured forensic inquiry – the analysis of DNA. (Jobling, 353) DNA is contained in all living things, and all DNA demonstrate variations amongst and within species, legal case links any biological matter has all its information and its origin. This paper discusses the application of the forensic science in solving the crimes in general and then narrows down to a relatively new concept Mitochondria DNA and discusses how it helps in solving the crime cases. In the end of the paper a summary of the whole topic is given, discussing the major points covered in the paper.

Application of DNA In Solving Crimes

The impact of forensic DNA identification technology in the criminal justice process is quick and extensive. In the mid of eighties ‘genetic fingerprinting’ was introduced in high profile cases of serious crime; till now a day’s regular use of ‘genetic profiling’ in most crime investigations. DNA recognition put up a vital role to the exposure of crime and to the edifice of examination cases for courtroom hearings. Such recognition typically engage the compilation of genetic material revealed at crime scenes, the profiling of DNA taken out from this matter,

and the assessment of the profile gained with offered DNA profiles of criminals held on a ‘forensic’ record.  Two main kinds of educational learning have added to current understandings of the course and penalties of these uses of molecular biology and bio-technology in the unlawful justice method.  The first kind of study, largely informed by an interest in the institutional correlates of large-scale socio-historical changes, has represented the developing uses of DNA profiling and the construction of DNA databases as the instantiation of more generic changes in the modes of control and control policies characteristic of recent and contemporary Western European and North American societies. From this standpoint, DNA profiling is seen to play a significant (but largely unanalyzed) part in the ‘new culture of crime control’ which has both been informed by the political and cultural values of late modern society and has in turn come to shape the ways in which this society has installed ‘…more intensive regimes of regulation, inspection and control…[whilst]…our civic culture becomes increasingly less tolerant and inclusive, increasingly less capable of trust.’ (Garland, 194-5)

Accordingly, DNA databases containing an increasing number of the genetic profiles of criminal suspects constitute ‘centers of calculation’ whose installation marks the growing extensiveness and intensity of bureaucratic surveillance in contemporary society – as one amongst the multiplicity of ways in which modern forms of government seek and use knowledge about their citizens in general and ‘suspect citizens’ in particular (Marx, 19). Here DNA profiles, databased as seemingly robust and resilient knowledge about such citizens, are characterized as part of a bio-surveillance apparatus to which can be submitted the material residue of the past, present and potentially future criminal conduct of the person profiled. Stenson (1993, 379) has written about the ways in which a variety of forms of surveillance both embodies and enhances such ‘specialized knowledge about crime and criminals’. And like others he uses Foucault’s (1979) original idea of ‘governmentality’ to assert that knowledge of such surveillance has effects on the self management of those whose actions and identities are captured by its gaze. The incorporation of genetic knowledge into such techniques of surveillance is then simply ‘…only one element within a complex of programmes which address the issue of crime control…’ (Hutchby, 41), and the contemporary crime control complex is seen to deploy DNA databasing as part of a technologically facilitated infrastructure of intelligence gathering aimed at effective detection, crime reduction and risk management.

Mitochondrial DNA

Mitochondrial DNA (mtDNA) is perfect for older, smaller or degraded samples. These energy producing mitochondria have their own DNA molecules that are used to create a DNA profile, which is called mitochondrial DNA or mtDNA. In humans, the mitochondrial DNA genome consists of about 16,000 DNA building blocks (base pairs), representing just a fraction of the total DNA in cells. Because mitochondria are structurally strong and protect the DNA they contain, mitochondrial DNA is useful for identifying victims of mass disasters, where the nuclear DNA in the cells could have been degraded or damaged. It is also often used in Cold Cases.  (Sykes, 17) Most cells in our bodies contain between 500 and 1000 copies of the mtDNA molecule, which makes it a lot easier to find and extract than nuclear DNA. The rise of mtDNA testing in the field of forensics means that cases that were previously thought hopeless, may now be resolved. Mitochondrial DNA in human cells is often more robust and more plentiful than nuclear DNA. MtDNA typing can be performed on hair shafts, bone, and teeth. As a result, mtDNA testing has been widely utilized by investigators in “cold case” police units. (Tyler-Smith, 98)

mtDNA shares many of the theoretical disadvantages of the Y chromosome: it is non-recombining, so indicators do not segregate independently, thereby reducing diversity; it is uniparentally inherited (through the mother), so all members of a matriline share a haplotype; and it shows marked population structure. Furthermore, there is the complication of heteroplasmy. The advantage of mtDNA lies in its copy number, which is between ~200 and 1,700 per cell; this means that it has a greater probability of survival than nuclear DNA does. Forensic applications include analysis of samples that are old or severely damaged, or low in DNA (such as hair shafts), and include historical criminal cases. The normal practice is to sequence two segments of the control region that are particularly polymorphic, known as hyper-variable segments I and II (HVSI, HVSII). SNPs outside the hyper-variable segments will increase the power of mtDNA typing. Rather than considering the average-match probability (which is high, at ~0.005–0.025), match significance is usually evaluated by the ‘counting method’ — how many times a specific sequence has been observed in a population database, with a correction for sampling error. (Sinha, 93) There has been criticism of the quality of some forensic datasets, on the   basis of highly improbable sequences that are detectable by phylogenetic analysis. Heteroplasmy can lead to different sequences being found between hairs or tissues in a single individual, and even along the length of a single hair shaft. Mutation, which distinguishes heteroplasmic types, is particularly common at some sites (‘hot spots’), but this can be built into the interpretation using a likelihood ratio approach. Shared heteroplasmy between two samples can actually increase the strength of evidence.

DNA and mtDNA Profile and Crime Solving

Once the crime has taken place, a complete from the crime scene is developed but when this profile does not seem to find any match in an intelligence database, whichever information that is able to be deducted from the DNA regarding the giver is of use. An essential bit of information required is sex, however two more characteristics are also helpful in investigating crimes which are: population of origin and phenotypic (physical) features.

Population Of Origin

In human population the genetic deviation is found to be the highest. However, people who `belong to different populations are, generally, somewhat additionally dissimilar from each other than are people from the similar population and this lets in setting of indicators to be used to calculate population of origin. Same techniques would be appropriate for the investigation of a crime scene sample. Forensic Short Tandem Repeat (STR) profiles are extremely inconsistent amongst people and therefore demonstrate little inter-population inconsistency (FST). They are as a result not perfect for calculating population of origin. The ability of SGM Plus profiles to classify people into one of five police-defined ‘ethnic groups’ has been evaluated, and proved. (Sinha, 103) Regardless of the misclassification, prediction is helpful if it decreases the amount of suspect investigations carried out prior to the real person responsible for has arrived. Police are not anthropologists and one difficulty with deducing these studies are the over simplified method in which populations are described. The haploid Y chromosome and mtDNA demonstrate strong geographic delineation for the reason that their small Effective Population Size (one quarter of that of any autosome) leads to improved Genetic Drift. Intercourse habits may as well add up to variation within population. These indicators as a result hold information on population of origin, however, due to admixture, can present deceptive outcomes. (Butler, 99)

Indicators with superior power have appeared from studies of admixed populations for epidemiological reasons or for planning ailment genes by Linkage Disequilibrium. Autosomal binary or STR loci have been recognized that demonstrate huge allele rate variations (30–50%) among parental population groups. Multilocus genotypes based on such Ancestry Informative Indicators (AIMS) can be investigated by means of model-based clustering algorithms, yielding individual shares of descent from a number of populations. (Macaulay,  315) even though forensic assessment has not yet been conceded out, tests using 175 AIMs are by now accessible from markets for forensic use; their use will perhaps enhance, while it might be restricted in admixed populations.

Phenotypic Information

A strong prediction of population of origin might indicate some aspects of phenotype, such as skin color. However, direct genetic tests would be more useful. Many human phenotypes (for example, stature, facial features and pigmentation) have a strong genetic component. The only relevant trait that has undergone serious investigation is pigmentation. However, although there are many human genes that when mutated are known to cause abnormal pigmentation such as albinism, only a minority appear to influence ‘normal’ variation. The best studied is the melanocortin 1 receptor (MC1R) gene, the gene product of which lies in the cell membrane of the Melanocyte. Binding of ?-melanocyte stimulating factor to the receptor leads to production of black/ brown pigments, whereas in the absence of a signal through MC1R, red/yellow pigments predominate. (Holland, Parsons, 21) The MC1R gene has more than 30 known variant alleles involving amino-acid substitutions, three of which are associated with red hair, fair skin and freckling. Population studies show that homozygosity or compound heterozygosity for such a variant gives a >90% probability of having red hair. This test is therefore useful as an investigative tool in populations where red hair is found at an appreciable frequency. Other candidate pigmentation genes have been investigated, but with less success. Linkage analysis has identified a locus on chromosome 15 that influences eye color, for which the P gene, the product of which is involved in melanin production, is a candidate. Two amino-acid substitutions in the gene are associated with blue or grey eyes. A broader association study including SNPs in several candidate genes has identified 61 SNPs that explain 15% of the variation in eye color in a sample, but probably do not provide useful predictive testing. Work on these and other phenotypes will probably increase in the future. However, the complexity of these quantitative traits, coupled with variability introduced by environmental and nutritional differences, means that even if the genes influencing them were identified there is no guarantee that simple deterministic tests would emerge.

Non-Human Species In Forensic Genetics

Forensic analysis of animal DNA has been used both when animal material (usually pet hairs) is found at crime scenes, and in investigations of the illegal trade in endangered species. Work on canine identification is mostly based on STRs developed for parentage testing, but also includes mtDNA profiling. In the endangered species field, species-specific methods target the gene that encodes cytochrome b of mtDNA. As with animal material, plant material can be associated with a crime scene and provide vital evidence. When morphology is uninformative, DNA could, in principle, offer species identification or a link to a specific place. However, in the analysis of plant DNA there is no easy equivalent of the widely studied animal mtDNA sequences (although regions of the chloroplast genome and the nuclear ribosomal RNA loci seem promising) and STRs in most species are poorly characterized. (Chakraborty, 139) PCR-based fingerprinting methods such as Random Amplified Polymorphic DNA (RAPD) can allow identification of plant strains and have been used in the analysis of mosses in a murder case, and in civil disputes over the identity of commercially valuable cultivars of strawberry and chilli. A species-specific PCR assay is available for Cannabis sativa and the isolation of a hexanucleotide STR from the same species provided a indicator with some potential to identify the source of cannabis samples. Microorganisms can be sources of evidence in situations such as foodstuff contamination and medical negligence cases involving infections, such as HIV transmission. Microbiologists, epidemiologists and forensic scientists have met to define problems and make recommendations, many of which will be expensive to implement.

Future Developments

Forensic genetics will continue to take advantage of technical developments in DNA analysis. A ‘sci-fi’ vision of a hand-held device (the ‘lab on a chip’) that would allow rapid DNA profiling at the crime scene is close to realization, with developments in micro-fabrication of capillary electrophoretic arrays; single integrated platforms that extract, amplify and sequence DNA have

already been developed, but it will be some time before such devices are validated for forensic use.

Summary

In this paper we have examined some of the ways in which the use of DNA  and mtDNA in criminal investigations has both contributed to and been shaped by the creation of a national DNA database (NDNAD). In particular, this paper has mapped a number of important scientific and technical, developments, which have together transformed the forensic use of DNA. Contemporary investigative practice now involves the routine search for DNA evidence, potentially at every one of the hundred of thousands of crime scenes attended by scene examiners, and the collection of DNA samples from all those suspected by the police of involvement in a recordable offence. Nevertheless, there remain many policy questions concerning the use of DNA and the mtDNA for crime investigation.  (Chakraborty, 141) These range in scope, but include: whether the use of the mtDNA sustains, or even enhances asserted inequities in the criminal justice system; whether tissue samples used for DNA profiling should be destroyed or retained along with the digital profiles; under what circumstances may the convicted be allowed to reopen cases to seek exoneration by DNA analysis; and what privacy rights are attached to information potentially recoverable from the biological materials held by the laboratories that supply profiles to the National DNA Database? These questions will not only structure future research on the NDNAD but will provide the foundations for debates about the important social, ethical and legal issues which are raised by the operation of this increasingly important police resource.

Works Cited

Butler, J. M. Recent developments in Y-Short Tandem Repeat and Y-Single Nucleotide Polymorphism analysis. Forensic Science Review. 15, 91–111 (2003).

Chakraborty, R. Forensics and mitochondrial DNA: applications, debates and foundations. Annual Revised. Genomics Human. Genetics. 4, 119–141 (2003).

Foucault, M. “Governmentality.” Ideology and Consciousness 6, 1979.

Garland, D.  The Culture of Crime Control. Oxford: Oxford University Press (2001).

Holland, M. M. & Parsons, T. J. Mitochondrial DNA sequence analysis — validation and use for forensic casework. Forensic Sci. Rev. 11, 21–49 (1999).

Hutchby, I. “Technologies, Texts and Affordances.” Sociology 35(2): 41-56 (2001).

Jobling, M. A. In the name of the father: surnames and genetics. Trends Genet. 17, 353–357 (2001).

Macaulay, V. The mitochondrial gene tree comes of age. Am. J. Hum. Genet. 68, 315–320 (2001).

Marx, G.T. “What’s New About the ‘New Surveillance’? Classifying for Change and Continuity.” Surveillance and Society 1: 9-29, 2002 .

Sinha, S. K. et al. Development and validation of a multiplexed Y-chromosome STR genotyping system, YPLEX 6, for forensic casework. J. Forensic Sci. 48, 93-103 (2003).

Stenson, K. “Community Policing as a Governmental Technology.” Economy and Society 22: 373-399, 1993.

Sykes, B. & Irven, C. Surnames and the Y chromosome. Am. J. Hum. Genet. 66, 17–19 (2000).

Tyler-Smith, C. The human Y chromosome: an evolutionary indicator comes of age. Nature Rev. Genet. 4, 98–102 (2003).

 

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