what are possible experimental problems could invalidate the results when you us

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nce Products > Product Articles > Life Science Technologies: LIFE SCIENCE TECHNOLOGIES 04 March 2011 Qiagen This Special Advertising Feature is brought to you by AAAS OPMS DOI: 10.1126/science.opms.p1000052 LIFE SCIENCE TECHNOLOGIES Forensics Follows New Clues For PDF versionNew Products picture Forensic DNA analysis has already revolutionized criminal investigation. Now researchers and toolmakers are building faster, more sensitive DNA fingerprinting platforms while adding entirely new techniques to detectives' toolkits. By Alan Dove Inclusion of companies in this article does not indicate endorsement by either AAAS or Science, nor is it meant to imply that their products or services are superior to those of other companies. On television, all forensic technology fits into a standard plotline. Someone commits a brilliant, dastardly crime, and a team of romantically entwined investigators—with limitless access to cutting-edge tools—finds and collars the perpetrator in under an hour, with time for commercial breaks. Reality, of course, is considerably messier. The majority of criminals are not especially brilliant, but even their rudimentary efforts to cover their tracks can make an investigator's job infuriatingly difficult. New technology might help, but only if crime labs can adopt it without breaking their budgets or having to retrain an entire staff. The problems are as diverse as the cases. DNA analysis forms the backbone of modern forensics, but labs processing DNA evidence operate under enormous technical and legal constraints. The slightest contamination of a sample, or just poor recordkeeping, can invalidate the evidence from multiple cases. Meanwhile, technicians are often working against the clock; if a prime suspect is in custody, there may be only a few hours to process evidence before he or she is released on bail. DNA fingerprinting isn't the only challenge, though. Out in the field, investigators spend a lot of time searching for bodies, and then trying to identify them even if they're badly decomposed. To address these problems, researchers working in corporate, university, and government labs are modifying established forensic technologies and are also developing entirely new ones. While some of the tools coming from this interdisciplinary field are targeted specifically at solving crimes, others may find a broad range of uses in basic and applied research. 1. Generating a High Probability The probability of a DNA fingerprint belonging to a specific person needs to be reasonably high--especially in criminal cases, where the association helps establish a suspect's guilt or innocence. Using certain rare VNTRs or combinations of VNTRs to create the VNTR pattern increases the probability that the two DNA samples do indeed match (as opposed to look alike, but not actually come from the same person) or correlate (in the case of parents and children). 2. Problems with Determining Probability A. Population Genetics VNTRs, because they are results of genetic inheritance, are not distributed evenly across all of human population. A given VNTR cannot, therefore, have a stable probability of occurrence; it will vary depending on an individual's genetic background. The difference in probabilities is particularly visible across racial lines. Some VNTRs that occur very frequently among Hispanics will occur very rarely among Caucasians or African-Americans. Currently, not enough is known about the VNTR frequency distributions among ethnic groups to determine accurate probabilities for individuals within those groups; the heterogeneous genetic composition of interracial individuals, who are growing in number, presents an entirely new set of questions. Further experimentation in this area, known as population genetics, has been surrounded with and hindered by controversy, because the idea of identifying people through genetic anomalies along racial lines comes alarmingly close to the eugenics and ethnic purification movements of the recent past, and, some argue, could provide a scientific basis for racial discrimination. B. Technical Difficulties Errors in the hybridization and probing process must also be figured into the probability, and often the idea of error is simply not acceptable. Most people will agree that an innocent person should not be sent to jail, a guilty person allowed to walk free, or a biological mother denied her legal right to custody of her children, simply because a lab technician did not conduct an experiment accurately. When the DNA sample available is minuscule, this is an important consideration, because there is not much room for error, especially if the analysis of the DNA sample involves amplification of the sample (creating a much larger sample of genetically identical DNA from what little material is available), because if the wrong DNA is amplified (i.e. a skin cell from the lab technician) the consequences can be profoundly detrimental. Until recently, the standards for determining DNA fingerprinting matches, and for laboratory security and accuracy which would minimize error, were neither stringent nor universally codified, causing a great deal of public outcry. Not Infallible Scientists consider DNA fingerprinting very accurate when done correctly. However, since humans play a significant part in the fingerprinting process, errors can occur in labs or at crime scenes. Cross contamination of a sample would give an inaccurate DNA fingerprint. DNA fingerprinting establishes only a statistical probability that samples match. DNA fingerprinting does not offer certainties, but comparing larger numbers of samples lower the possibility of mistakes. Intrusive Your DNA is very personal, perhaps more personal than any other type of identification.Your DNA can tell others every medical condition you have or could develop. If others gain access to this information, it would constitute an invasion of your privacy. Computers often store DNA fingerprinting results, which always raise concerns about privacy of personal information. If hackers gained access to a database storing DNA fingerprints, they would have access to extremely personal information. Discrimination Due to the personal nature of the information provided by DNA fingerprinting, undue discrimination could result from misuse of this information. Your DNA serves as a blueprint for your medical history and your potential for future conditions. Misuse of this information could include discrimination by insurance companies (who might refuse coverage) or employers (who might refuse to hire employees with undesirable DNA).

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