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Forensic Serology Identification Using Blood Groups.

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Presentation on theme: "Forensic Serology Identification Using Blood Groups."— Presentation transcript:

1 Forensic Serology Identification Using Blood Groups

2 Forensic Serology Serology – term used to describe a broad range of laboratory tests using reactions of blood serum and body fluid (including saliva, semen, urine, and blood) 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 Due to funding & time needed for DNA analysis, many labs focus on basic serology procedures

3 The Composition of Blood Blood is a mixture of many components: cellsinorganic substances (salts) enzymeswater proteins 55 % of blood content is plasma – mostly water and substances dissolved in it Most of the solid materials (by weight, 45%) are cells red blood cells, RBCs (erythrocytes): deliver oxygen white blood cells (leukocytes): immune system platelets (thrombocytes): used for clotting

4 Blood Terminology ABO blood groups—based on having an A, B, both or no antigens on red blood cells Rh factor—may be present on red blood cells; positive if present and negative if not Antigen—a substance that can stimulate the body to make antibodies. Certain antigens (proteins) found in the plasma of the red blood cell’s membrane account for blood type. Antibody—a substance that reacts with an antigen Agglutination—clumping of red blood cells; will result if blood types with different antigens are mixed

5 Forensic Characterization of Bloodstains Three questions that must be answered by the forensic investigator: 1) Is it blood? (most of these detect heme) Kastle-Meyer Test Hemastix (o-tolidine, TMB) Luminol Test 2) Is it human blood? Precipitin Test 3) Can it be associated with an individual? -look at blood type, alcohol content, and drugs present

6 Is it Blood? Tests Kastle-Meyer Test –Inexpensive –Easy to perform –Add H2O2 to blood, Heme breaks apart, add phenolphthalein to show pink color –Quick results –Provides evidence if red spots found at a crime scene are actually blood Other substances (vegetables) can give a positive result, must be careful

7 Is it Blood? Tests Hemastix/ Hematest tablet –This test involves a plastic strip with a reagent-treated filter paper tab at the end that contains Tetramethylbenzidine (TMB) and hydrogen peroxide (H 2 O 2 ) –Moisten a cotton swab with distilled water, touch the swab to the stain and place the swab directly onto the reagent tab on the strip –The reagent tab is originally yellow and undergoes a color change to green or blue- green indicating the presumption of blood

8 Luminol Red blood cells contain hemoglobin (Hb) – the protein responsible for transporting oxygen Each Hb contains four iron (Fe) containing hemes Wherever the luminol touches blood, it glows, and the glow is bright enough to be photographed Heme structure Scientists usually use luminol as a last resort because it can damage DNA evidence in blood

9 Precipitin Test Blood of every species contains different proteins, and blood from one species will not accept blood from another -test is time sensitive, but does work on small traces of blood

10 Animal Blood Larger nucleic red blood cells Frog Blood

11 Human Blood Red blood cells are most numerous; 5 to 6 million per mm 3 White blood cells are larger and less numerous; 5 to 10,000 per mm 3 Platelets are tiny, cellular fragments; 350 to 500,00 per mm 3

12 Blood Antigens On the surface of red blood cells are chemical structures (proteins) called antigens 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

13 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

14 Blood Groups Type Antigen Antibody Can Give Blood To Can Get Blood From A B AB O A B A and B Neither A nor B B A Neither A nor B A and B A, ABO, A B, ABO, B AB A, B, O, AB O

15 Population Distribution of Blood Types in the U.S. TypePercent O A B AB 45 40 11 4

16 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

17 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

18 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?

19 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? O positive

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

21 Projected Bloodstain Analysis Two Important Determinations: a. direction of splatter b. angle of impact with surface

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