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Forensic Serology

Forensic Serology

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Forensic Serology

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  1. Forensic Serology Forensic Science

  2. Composition of Blood • Blood is a complex mixture of cells, enzymes, proteins, and inorganic substances • Main Components: • Erythrocytes = red blood cells (RBCs) • Leukocytes = white blood cells (WBCs) • Platelets= clotting factors • Plasma = the liquid part

  3. Antigens and Antibodies • Antigens: proteins on surface of cells (including RBCs) that identify them • Different types of cells have different antigens • Antibodies: Y-shaped immune system proteins that recognize and bind to foreign objects to neutralize them • You get vaccines to develop these! • Agglutination: clumping of antibodies when they bind to their specific antigen

  4. ABO Blood System • Anti-A antibodies will agglutinate (clump) in Type A blood • Anti-B antibodies will agglutinate in Type B blood • Type AB blood will agglutinate in anti-A or anti-B serum • Type O blood will not cause agglutination

  5. Blood Donors and Recipients BLOOD TYPEDONATES TORECEIVES FROM A A, AB A, O B B,AB B, O AB ABA, B, AB, O O A, B, AB, O O • Type AB blood is the universal recipient because it can take any of the 4 types and not agglutinate • Type O (most common) is the universal donor it does not have any antigens to cause agglutination

  6. Rh Factor • Rh (Rhesus) factor is another important blood antigen • This is the positive (+) and negative (-) of blood types • Rh- means you don’t have the antigen • Rh factor affects blood donation compatibility • Rh+ blood types can accept either Rh+ or Rh- • Rh- can only accept Rh- blood or it will agglutinate

  7. Genetics of Blood • Blood types are determined by looking at 2 inherited genes (one from each parent) • There are 3 common alleles for blood types: A, B, and O, with 6 possible combinations BLOOD TYPEALLELE COMBINATIONS A AA, AO B BB, BO AB AB O OO Punnett Square

  8. (stop) Blood Typing Lab

  9. Blood Stain Analysis Forensic Science

  10. Testing for Blood When they find a red stain, investigators must ask themselves 3 questions: Is it blood? Is it human blood? Whose blood is it?

  11. Presumptive tests (color tests) indicate the presence of blood Kastle-Meyer: this solution of phenolphthalein turns bright pink when it encounters the blood protein hemoglobin Some vegetable matter like potatoes and horseradish can give a positive K-M result, but… you’re probably not going to find those at a crime scene Is it blood?

  12. Is it blood? Luminol: When sprayed on blood, this solution produces a faint blue light This can work on blood that someone tried to clean up

  13. (Luminol demos)

  14. Is it human or animal blood? Precipitin Test Serum made in rabbit contains antibodies against human blood Crime scene blood is layered on top of the anti-human serum in a test tube If the sample is positive for human blood, a cloudy precipitate will form where the 2 layers meet

  15. Whose blood is it? A DNA analysis would have to be performed to find out exactly who the blood belongs to But ABO blood typing can narrow down a pool of suspects.

  16. Blood Spatter Analysis Passive Dripping Transfer Impact Spatter: Occurs when an object impacts a source of blood

  17. Blood Spatter Analysis Blood spatter patterns can be used to re-create a crime scene. It is possible to determine: The direction the blood was travelling The angle of impact The point of origin of the blood This can help determine the manner of death

  18. Blood Spatter Analysis - Surface When examining blood spatter, is it important to consider the surface Hard and nonporous surfaces like glass and tile generally result in round drops with less spatter Rough surfaces like carpeting, wood, or fabric usually result in irregularly shaped stains with serrated edges and possibly satellite spatter Satellite spatter are the tiny droplets that break away from the main drop

  19. Blood Spatter Analysis - Speed Size of blood drops tells us about the speed of the drop upon impact Small droplets (less than 1 mm; spray) mean high velocity around 100 ft/s Example: gunshot wound Medium droplets (1-4 mm) mean medium velocity around 25 ft/s Example: stabbing Large droplets (4-6 mm) mean low velocity around 5 ft/s Example: blunt object impact such as a hammer to the head

  20. Blood Spatter Analysis - Height • How far from the ground a blood drop originated is reflected in the size of the blood drop. • A drop from farther up will spread out more upon impact.

  21. (stop) Lab: Affect of Height on Size of Blood Drops

  22. Blood Spatter Analysis - Direction Momentum tends to keep blood moving the direction it was traveling In an elongated blood drop, the tail points in the direction of the blood’s movement Satellite droplets appear in front of the moving droplet of blood direction of movement

  23. Blood Spatter Analysis - Angle The angle of impact can be found mathematically Divide the width (shorter side) of the blood drop by the length (longest part) Then take the inverse sin, also called “arcsin” or “sin-1”of that number to get the angle. angle = arcsin (width/length)

  24. Blood Spatter Analysis - Angle The smaller the angle (meaning the source was closer to the floor) the longer and more stretched the blood drop looks

  25. Blood Spatter Analysis - Convergence You can figure out where blood came from by drawing lines through the long axis of the droplet. Remember the tail (and satellites) indicate the direction blood was moving, so the origin is the opposite direction. Where lines meet is called the area of convergence.

  26. area of convergence

  27. Blood Spatter Analysis – Origin Lines of convergence give you a direction that blood came from, but not height. You can use the angle of impact and trigonometry to determine how far up the blood came from

  28. Blood Spatter Analysis - Origin Use angle of impact and convergence lines to make an imaginary right triangle You know the angle of impact, you know the “adjacent” side length Solve for height using the Law of Tangents

  29. Remember SOH CAH TOA Tangent is opposite/adjacent tanθ = height/distance to convergence so height = tanθ x distance height =tan27°x 5.75 ft height = 0.5095 x 5.75 ft height = ~2.9 ft above the ground hypotenuse opposite angle adjacent Yay math!

  30. Add this formula to your notes… To find the height of the origin of blood spatter… height = tanθ x distance to convergence

  31. Blood Spatter Analysis - Origin You can use string to help you recreate point of origin There are also computer programs to help “No More Strings” DEXTER

  32. Blood Analysis – Wrap Up Ask: Is it blood? Is it human blood? Whose blood is it? Figure out: Speed of impact Angle of impact Area of convergence Point of origin • CLASS CHARACTERISTICS: • species • blood type • Rh factor • diseases? • INDIVIDUAL CHARACTERISTICS • DNA profile

  33. (stop)

  34. Forensic Serology:Other Body Fluids

  35. Other Body Fluids: Saliva • Consists of water, mucin for lubrication, amylase enzyme for digestion, buccal (cheek) cells that could provide DNA • Saliva is often associated with sexual assaults and bite mark evidence • Presumptive tests for saliva check for the amylase enzyme

  36. Other Body Fluids: Semen • Consists of water, spermatozoa, enzymes, salts • Semen is often evidence in sexual assault cases • Presumptive tests for semen include • Black light fluorescence • Chemical test for acid phosphatase (enzyme from prostate), turns purple when present • Confirmatory tests include microscopic examination for presence of sperm • DNA analysis can individualize the sample

  37. Other Body Fluids: Urine • Urine is composed mostly of water, and also includes urea (nitrogenous compound) and salts. • Urine is most often used for the detection of drugs in the body • EMIT (Enzyme-Multiplied Immunoassay Technique) test reveals the presence of specific drugs through antibody binding

  38. (end)

  39. Resources • 0135158494, Saferstein, Richard. Forensic Science: An Introduction. New Jersey: Pearson Prentice Hall, 2011. • 0536522820, Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 8th ed. Upper Saddle River, NJ; Pearson Prentice Hall, 2004. • Sam Sheppard by Fred McGunagle