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FORENSIC SEROLOGY

FORENSIC SEROLOGY

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FORENSIC SEROLOGY

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  1. FORENSIC SEROLOGY Chapter 8

  2. Nature of Blood • Blood is a highly complex mixture of cells, enzymes, proteins, and inorganic substances. • Plasma, is the fluid portion of blood and composed principally of water. • Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are the solid materials suspended in plasma. • Antigens, (proteins) are located on the surface of red blood cells and are responsible for blood-type characteristics. FORENSIC SEROLOGY

  3. Blood Typing • More than 15 blood antigen systems have been identified, but the A-B-O and Rh systems are the most important. • An individual that is type A has A antigens on his/her red blood cells, type B has B antigens, AB has both A and B antigens, and type O has neither A nor B antigens. • Rh factor is determined by the presence of another antigen, the D antigen. • People having the D antigen are Rh positive; those not having the antigen are Rh negative. • For every antigen there is a specific antibody that will react with it to form clumps known as agglutination. • Thus, if serum containing anti-B is added to red blood cells carrying B antigen, they will immediately react. FORENSIC SEROLOGY

  4. HISTORY OF BLOOD TYPING • Early transfusions were direct (from one person to another) • 90% of tranfusion patients died before transfusion was finished • Landsteiner looked at the blood of failed transfusions and noticed clumping of blood cells • Discovered A-B-O system of surface proteins in FRESH blood • Lattes discovered a way to determine blood type from dried blood • Rh factor named for Rhesus monkey • Other surface proteins include: Minnesota, Lutheran, Kell, HLA

  5. Serology • The term serology is used to describe a broad scope of laboratory tests that use specific antigen and serum antibody reactions. • The identity of each of the four A-B-O blood groups can be established by testing the blood with anti-A and anti-B sera. • The concept of specific antigen–antibody reactions has been applied to immunoassay techniques for the detection of drugs of abuse in blood and urine. FORENSIC SEROLOGY

  6. Immunoassay • A number of immunoassay techniques are commercially available for detecting drugs through antigen-antibody reaction. • One is Enzyme-Multiplied Immunoassay Technique (EMIT), is speedy and very sensitive detecting drugs in urine. • In EMIT analysis, antibodies that will bind to a specific drug are added to the subject’s urine (Ch 6). • Radioimmunoassay (RIA), use drugs labeled with radioactive tags. FORENSIC SEROLOGY

  7. Antigen-Antibody Reaction • When an animal, such as a rabbit or mouse, is injected with an antigen its body will produce a series of different antibodies, all of which are designed to attack some particular site on the antigen of interest. • This collection of antibodies is known as polyclonal antibodies. • A specific collection of antibodies designed to combine with a single antigen site can be also be made and are known as monoclonals. FORENSIC SEROLOGY

  8. Forensics of Blood The criminalist must answer the following three questions when examining suspected bloodstains: 1. Is it blood? 2. From what species did the blood originate? 3. If the blood is of human origin, how closely can it be associated to a particular individual? Question #1 can be answered by a color test. FORENSIC SEROLOGY Presumptive blood test

  9. Color Tests • The Kastle-Meyer color test uses phenolphthalein to detect blood. • Hemoglobin causes a deep pink color. • Luminol test can detect blood diluted up to 300,000 times. • Produces blue glow (luminescence) in a darkened area. • Microcrystalline tests, Takayama and Teichmann, uses chemicals that form crystals if blood is present. Not very sensitive. Easily contaminated. FORENSIC SEROLOGY Luminol Test

  10. The Tests Question # 2: • Precipitin test uses antibodies from rabbits that have been injected with the blood of a known animal to determine the species of a questioned bloodstain. Question #3: if the bloodstain is human, it must be matched to the crime scene, either the victim or suspect(s). • DNA analysis has allowed forensic scientists to match blood to a single individual. • Before 1990’s, ABO blood typing could only be used to eliminate a suspect, but could not be used to convict them. FORENSIC SEROLOGY

  11. Stain Patterns of Blood • The location, distribution, and appearance of bloodstains and spatters give useful information for reconstructing the events that produced the blood. • Surface texture and the stain’s shape, size, and location must be considered when determining the direction, dropping distance, and angle of impact of a bloodstain. FORENSIC SEROLOGY

  12. Stain Patterns of Blood • The harder and less porous the surface, the less blood spatter. • The direction of travel of blood striking an object is determined by the pointed end of a bloodstain which always points in the direction of travel. • The impact angle of blood on a flat surface at right angles shows a circular spot, as the angle decreases-the stain becomes more oval. • The origin of a blood spatter in a two-dimensional projection can be established by drawing straight lines through the long axis of several individual drops The intersection or point of convergence of these lines represents the origin point. FORENSIC SEROLOGY

  13. Heredity and Paternity • The transfer of hereditary material is accomplished by means of units called genes, located on chromosomes. • Alleles: Alternative forms of genes that influence a given characteristic (such as eye color or blood type). • Paternity testing has historically involved the A-B-O blood typing system, along with blood factors such as Rh (D). • DNA test procedures raise the odds of establishing paternity beyond 99%. FORENSIC SEROLOGY

  14. Testing for Seminal Stains • Many of the cases sent to a forensic laboratory involve sexual offenses, making it necessary to examine exhibits for the presence of seminal stains. • The best way to locate and at the same time characterize a seminal stain is to perform the acid phosphatase (an enzyme found in seminal fluid) color test. • A purple color indicates acid phosphatase enzyme. • Semen are identified by either the presence of spermatozoa or of p30, a protein unique to seminal plasma. • Forensic scientists can link seminal material to an individual by DNA typing. FORENSIC SEROLOGY

  15. Blood Evidence • WET blood items are collected and packaged in paper to prevent mold and bacteria growth. Wet spots can be collected with sterile dry swabs and packaged in paper. • Dried blood can be collected with a sterile swab and either sterile water or saline solution and packaged in plastic vials or tubes. • Large areas such as bedding or carpeting can be cut to obtain stained AND UNSTAINED control samples • WET items MUST be unpacked at the lab and AIR DRIED in a controlled environment. FORENSIC SEROLOGY