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Forensic Serology

Forensic Serology. Chapter 10. Blood Components. Plasma—fluid part of unclotted blood Erythrocytes—”red” cells that hold hemoglobin and transport oxygen Leukocytes—immune “white” cells Platelets —cell fragments that cause clotting Serum—yellow fluid that remains after clotting of blood.

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Forensic Serology

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  1. Forensic Serology Chapter 10

  2. Blood Components • Plasma—fluid part of unclotted blood • Erythrocytes—”red” cells that hold hemoglobin and transport oxygen • Leukocytes—immune “white” cells • Platelets—cell fragments that cause clotting • Serum—yellow fluid that remains after clotting of blood

  3. Antigens and Antibodies • Antigen: • A substance, usually a protein, that causes an immune reaction in the body • Located on the outside of cells • Antibody • Produced by body to bind with specific antigens • One antibody per antigen • Antibodies are produced for foreign proteins • A, B, Rh (D) are antigens

  4. Blood Types • Blood Type A has A antigens and B antibodies • Blood Type B has B antigens and A antibodies • Blood Type AB has both A and B antigens and no antibodies • Blood Type O does not have any antigens but both A and B antibodies • Rh+ blood has D antigens • Rh- blood does not have Rh(D) antigens but has D antibodies

  5. Serology • Rh+ blood will agglutinate with Anti-D serum • Rh- blood will not agglutinate with Anti-D serum • A blood will agglutinate with Anti-A serum • B blood will agglutinate with Anti-B serum • AB blood will agglutinate with both anti-A and anti-B serum • O blood will not agglutinate with anti A or anti B • http://www.youtube.com/watch?v=E0d5Qx42vmQ

  6. Immunoassay techniques • Used to detect drugs in blood and urine • Animals are injected with proteins with drug antigens—animal makes drug detecting antibodies that can be harvested • Presumptive drug testing with these cultured antibodies can be used to detect opiates, cannabinoids, cocaine, amphetamines, phencyclidine, barbituates and methodone

  7. Producing Antibodies • Radioimmunoassay (RIA)—uses radioactive tags to find drugs • Enzyme-Multiplied Immunoassay Technique (EMIT)—fast and used with urine; adds antibodies to urine that bind to specific drugs • Polyclonal and Monoclonal Antibodies—animals produce many different kinds (polyclonal) of antibodies when exposed • Scientists need one kind of antibody (monoclonal) • Produce monoclonal antibodies using hybridoma cells (spleen cells fused with cancer cells)

  8. Genetics of Blood Typing • Blood type is a genetic trait • Encoded in DNA • DNA is grouped in chromosomes • Humans have 46 chromosomes: 23 from mother, 23 from father • Chromosomes contain genes • Alleles are versions of a gene • Genes can be dominant or recessive

  9. Paternity Testing with Blood Type • Determined by 3 alleles: • A, B, O • A Blood Type—AA or AO • B Blood Type—BB or BO • O Blood Type—OO • AB Blood Type—AB • Parent gives each offspring one of two alleles • Genes of child must come from parents

  10. Blood Stain Analysis • 3 Questions • Is it blood? • Is it human? • Can it be matched closely to a particular person?

  11. Presumptive Color Testing • Benzadine color test • Detects presence of hemoglobin • Reduced use because carcinogenic • Kastle-Meyer— • Phenolphthalein indicator • Turns pink when mixed with hydrogen peroxide and catalase • Blood, horseradish, animal material all contain catalase • http://www.youtube.com/watch?v=6Ex0Fd_PDhU

  12. Luminol • Presumptive blood test • Reaction with blood emits light • Spray on suspected area, turn out lights, see blue light • http://www.youtube.com/watch?v=hbEHvRrfqrc

  13. Microcrystalline Tests • Oldest method of blood detection • Takayama test • Teichmann tests • Add chemicals to blood that causes crystals to form with hemoglobin • Susceptible to interference from contaminants • Less sensitive than color tests

  14. Precipitin Test • Used to determine if blood stain is human or animal • Inject human blood into rabbit to produce antibodies • Create human antiserum from rabbit blood • Human antiserum reacts with human blood to produce precipitate • Can also create dog, horse, other animal antiserum

  15. Gel Diffusion with Precipitin • Use agar gel • Blood and human antiserum are loaded into wells • Antibodies and antigens come together in medium plate • Precipitate forms between two wells if blood is human • Electrophoretic method uses electric field to speed up the process

  16. Blood Spatter • Important Blood Qualities to Interpret Blood Spatter • Surface texture—more spatter with softer porous material • Direction of travel—pointed end faces direction of travel • Impact angle—right angle yields circular stain • Origin of spatter—draw lines through many spatter points; point of intersection is origin of spatter • http://www.youtube.com/watch?v=Od8YuwUT794

  17. Forensic Analysis of Semen • Tests for Presence of Semen • Acid Phosphatase Test • acid phosphatase is an enzyme made by the prostate gland • 400x more concentrated in semen • acidic sodium alpha napthylphosphate + fast blue dye + acid phosphatase = turns purple • 4-methyl umbelliferyl phosphate + acid phosphatase = fluoresces in UV light • Microscopic examination • Dissolve stain in water • Look for presence of sperm cells • Prostate specific antigen • Grow polyclonal antibodies to PSA in rabbits • Gel electrophoresis • Use monoclonal antibodies with dye

  18. Rape Evidence Collection • Rape Kit Collection from victims • Hair samples: head, pubic, body • Body opening swabs: vagina, anus, mouth (as needed) • Dry skin swabs (as needed) • Blood sample • Fingernail scrapings • All clothing (store in paper) • Urine sample • Collected from male suspects • All clothing • Hair: head, pubic, and body • Genital swab • Blood sample • Cheek cells

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