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Forensic Serology

Forensic Serology. Identification Using Blood Groups. This presentation contains graphic pictures. Forensic Serology. Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid.

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Forensic Serology

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  1. Forensic Serology Identification Using Blood Groups This presentation contains graphic pictures.

  2. Forensic Serology Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid • The serology section of a forensic laboratory may deal with any or all of the following: • blood typing • characterization of unknown blood • stain patterns for crime reconstruction • paternity testing • semen identification in rape cases • DNA techniques used for identification

  3. The Composition of Blood Blood is a mixture of many components: cells inorganic substances (salts) enzymes water proteins 55 % of blood content is plasma – mostly water and substances dissolved in it Most of the solid materials (by weight) are cells red blood cells, RBCs (erythrocytes) white blood cells (leukocytes)

  4. Forensic Characterization of Bloodstains Three questions that must be answered by the forensic investigator: 1) Is it blood? Benzidine Test Kastle-Meyer Test Hemastix (o-tolidine, TMB) Luminol Test 2) Is it human blood? Precipitin Test 3) Can it be associated with an individual?

  5. Luminol • Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen • Each Hb contains four iron (Fe) containing hemes Heme structure

  6. Luminol • Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen • Each Hb contains four iron (Fe) containing hemes Heme structure

  7. Forensic Characterization of Bloodstains Three questions that must be answers by forensic investigator: 1) Is it blood? Benzidine Test Kastle-Meyer Test Hemastix (o-tolidine, TMB) Luminol Test Enzymatic Tests 2) Is it human blood? Precipitin Test 3) Can it be associated with an individual?

  8. Precipitin Test

  9. Blood Antigens On the surface of red blood cells are chemical structures (proteins) calledantigens The presence of antigens allow a living system to recognize foreign biological substances Antigens also impart specific characteristics to the red blood cells. These characteristics can be partly used to identify individuals Human red blood cells have more than 15 different antigen types that have been discovered

  10. Blood Typing Blood typing involves determination of the antigens present on an individual’s RBCs The two most common blood typing systems used are the A-B-O method and the Rh method type A blood – contain “A” antigen on RBCs type B blood – contain “B” antigen on RBCs type AB blood – contains both A and B antigens type O blood – contain no A or B antigens Rh+ blood – contain Rh antigen Rh- blood – no Rh antigen

  11. Blood Typing Blood also contains antibodies –proteins that recognize and bind to certain, specific antigens Blood TypeAntigens on RBCAntibodies A A anti-B B B anti-A AB AB none O none both A & B

  12. Blood Typing When blood containing a specific antigen is mixed with blood containing the corresponding antibodies, the blood clots The clots can then be removed by the host system

  13. Blood Typing Human serum containing specific antibodies can be purchased Separately mix a drop of unknown blood sample with drop of each anti-serum Reaction between blood and anti-serum No reaction between blood and anti-serum

  14. Blood Typing Example A sample of unknown blood is mixed with three anti-sera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample? The ABO antigens are not confined to RBC; 80% of Americans are secretors, found on other cells

  15. Blood Typing Example A sample of unknown blood is mixed with three anti-sera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample? The ABO antigens are not confined to RBC; 80% of Americans are secretors, same antigens found on other cells O positive

  16. Blood Splatter Analysis Categories of Bloodstains: Passive (dripping) Transfer (smearing) Projected Projected Bloodstains occur in shootings, trauma from blunt weapons, hacking, or slashing attacks.

  17. Projected Bloodstain Analysis Two Important Determinations: a. direction of splatter b. angle of impact with surface sin  = (width drop / length drop)

  18. Forensic Characterization of Semen • Many crimes involve sexual misconduct • Normal males, upon ejaculation, release seminal fluid. This fluid is a mixture of components: • water • spermatozoa • enzymes • inorganic salts • Semen at a crime scene (clothing, bed sheets, carpet, cushions) can be located and identified by three common methods: • microscope examination to find sperm • acid phosphatase test • p30 (also called prostrate specific antigen) immunoassay test

  19. Forensic Characterization of Saliva Saliva is a mixture of many components: 99% water Mucin (protein helps in swallowing) Amylase (enzyme to help digest carbohydrates) Cheek cells (good for DNA) Adults produce 1.0-1.5 liters of saliva/day and it is not uncommon at crime scenes (especially involving bite marks). A simple test for saliva involves mixing starch, iodine, and a sample of the presumed saliva together. Starch and iodine are a deep blue color when mixed together. The amylase breaks down starch, however, and the color fades (takes about 15 mins @ 37 oC).

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