Multisystem method (Forensic Science)
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...
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Further Reading (Forensic Science)
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.
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Multisystem Method (World of Forensic Science)
Serologists (scientists who study blood serum, and immune factors in blood serum) Brian Wraxall and Mark Stolorow pioneered the "multisystem method" for the simultaneous separation of three isoenzymes (glyoxalase I, esterase D, and phosphoglucomutase) from bloodstains in 1978. They also created and developed a multisystem method involving the use of electrophoresis analysis and an immunoelectrophoretic technique for use in forensic identification of bloodstains. The goal of the multi-system method is to carry out several different procedures simultaneously, thereby vastly reducing the amount of bloodstain needed for the analysis (cutting it by two-thirds), multiplying accuracy, markedly reducing the time previously involved in the sequential analysis of all three isoenzyme components, and accomplishing all of this without any loss in sensitivity or resolution.
Blood remains the single most important type of evidence in the world of forensic science and of criminal investigation. It can link perpetrator to act of violence, to victim, to crime scene, and to other evidence. A bloodstain is first typed for blood group. While quite useful, this is considered only class evidence (evidence that links to a specific group), as it can exclude suspects, but cannot conclusively identify a specific individual. At a slightly higher level of sophistication, the sample can then be typed for Rh factor, and sub-grouped beyond this.
In order to type the stain to the greatest possible level of specificity, with the goal of accurately linking a sample or bloodstain to a single individual, the typing of proteins and enzymes is utilized. Blood proteins and enzymes share the characteristics of isoenzymes, or polymorphisms; that is, they exist in multiple molecular forms that have the same or very nearly identical enzyme activities and therefore, they have subtypes. Among the more common isoenzymes found in blood (and in bloodstains) are: transferrin, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, esterase D, adenyl kinase, glutamic pyruvate transaminase, glyoxalase I, erythrocyte acid phosphatase, adenosine deaminase, and phosphoglucomutase. Each isoenzyme, as well as every blood group subtype, has a known population distribution. By breaking the blood sample down to the level of maximum specificity, it is possible to progressively exclude the population of suspects until only one individual is left who could possibly match the set of specific blood group, type, and polymorphism markers. For example: the sample and the suspected perpetrator both have blood type A (42% of the population), and basic subtype A2 (25%), protein adenyl kinase (15%), and enzyme phosphoglucomutase (6%). The probability that there could be two individuals with this exact blood type is: (0.42 x 0.25 x 0.15 x 0.06), or less than 0.000945 percent.
By creating multisystem methods for bloodstain typing, Wraxall and Stolorow revolutionized the field of individualized blood typing, and made lasting contributions to the accuracy, validity, and reliability of forensic science, by dramatically decreasing required sample size, increasing efficiency and saving considerable cost by allowing for the simultaneous testing of three isoenzymes, and doing so without sacrificing either resolution or accuracy.
SEE ALSO Antibody; Antigen; Bloodstain evidence.