Multisystem method in bloodstain analysis
The multisystem method in bloodstain analysis is a forensic technique designed to identify individuals based on the unique proteins present in their blood. This method enhances the identification process beyond the basic ABO blood typing, which is often too general to conclusively pinpoint a suspect. By focusing on blood proteins, particularly isozymes—variations of enzymes that differ genetically among individuals—this approach allows forensic analysts to exploit the polymorphic nature of DNA sequences that encode these proteins.
Developed in 1978 by forensic scientists Brian Wraxall and Mark Stolorow, the multisystem method employs electrophoresis to separate blood proteins in a gel medium. This technique is notable for its efficiency, as it enables the simultaneous analysis of three different isozymes from a single bloodstain, significantly reducing both the material needed for analysis and the time required to complete the tests. The identification process involves comparing the patterns of isozymes, which are unique to individuals (with the exception of identical twins), thereby increasing the likelihood of accurately linking a bloodstain to a specific person.
Ultimately, the multisystem method contributes to forensic investigations by progressively excluding potential suspects based on the known frequencies of isozymes in different populations, aiming to narrow down to a single individual with the highest probability of matching the blood evidence. This method exemplifies the intersection of science and justice in criminal investigations, underscoring the importance of meticulous blood analysis in solving crimes.
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Multisystem method in bloodstain analysis
Definition: Laboratory technique that uses electrophoresis and enzymatic activity stains simultaneously to identify isozymes of three different blood proteins from bloodstains.
Significance: The multisystem method for bloodstain analysis revolutionized bloodstain typing in forensic science. By making it possible to test for several isozymes from crime scene bloodstains simultaneously, it dramatically decreased sample sizes, increased efficiency, and reduced the costs of analyses without sacrificing resolution or accuracy.
Bloodstain evidence is critically important to criminal investigators. Analysis of crime scene blood begins with the identification of the ABO blood type, which is useful but too vague to identify a particular suspect conclusively. Tests with greater specificity are required to identify the person from whom a bloodstain originated with a high probability.
Blood proteins are abundant and sometimes quite stable in dried blood and provide the means to identify a specific suspect. Many blood proteins are encoded by genes whose DNA (deoxyribonucleic acid) sequences are polymorphic—that is, they differ from person to person. These different forms of the same gene are called alleles. Different alleles encode proteins called isozymes that possess roughly the same biological functions but have slightly different physical properties.
Blood isozymes are analyzed by means of electrophoresis, a laboratory procedure that separates protein molecules on the basis of their size and charge. A portion of a dried blood sample is dissolved in water and loaded into a gel medium that is immersed in an ionized buffer solution. The application of an electrical current through the solution initiates the migration of the proteins through the gel medium, but each protein migrates in a distinct direction and at a distinct rate. Protein electrophoresis results in a pattern that can be fixed, stained, and interpreted by an analyst. The varying isozymes of numerous blood enzymes and protein systems make it unlikely that any two individuals, except identical twins, would possess identical enzyme and protein constitutions.
In 1978, two American forensic scientists, Brian Wraxall and Mark Stolorow, developed the multisystem method that simultaneously analyzed three different blood isozymes from the same bloodstain. After separating blood proteins by electrophoresis in a starch/agarose gel mixture, they used activity stains that specifically colored one particular enzyme and all its isozymes. By consecutively staining the gel with three different activity stains, Wraxall and Stolorow analyzed three proteins with one technique, reducing by two-thirds the quantity of material required for the test and also the time necessary to conduct it.
The goal of forensic blood analysis is to link a bloodstain to an individual with the highest possible probability. Because each isozyme occurs at a known frequency within particular populations, it is possible to exclude persons from the pool of suspects progressively until only one individual is left who could possibly match the set of specific blood group, type, and isozymes.
Bibliography
Rainis, Kenneth G. Blood and DNA Evidence: Crime-Solving Science Experiments. Berkeley Heights, N.J.: Enslow, 2007.
Wilson, Colin. Written in Blood: A History of Forensic Detection. New York: Carroll & Graf, 2003.
Wraxall, Brian, and Mark Stolorow. “The Simultaneous Separation of the Enzymes Glyoxalase I, Esterase D, and Phosphoglucomutase.” Journal of Forensic Sciences 31, no. 4 (1986): 1439-1449.