Forensic Serology


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Forensic Serology

  1. 1. Forensic Serology Nature of Blood Identification Tool Blood Spatter
  2. 2. Nature of Blood <ul><li>blood </li></ul><ul><ul><li>mixture of cells, enzymes, proteins and inorganic substances </li></ul></ul><ul><ul><li>for forensic science, red blood cells and serum are most important </li></ul></ul>
  3. 3. Blood as an Identification Tool <ul><li>Blood Typing </li></ul><ul><ul><li>by ascertaining the antigens present on the surface of red blood cells, blood can be typed </li></ul></ul><ul><ul><ul><li>A positive or A negative </li></ul></ul></ul><ul><ul><ul><li>B positive or B negative </li></ul></ul></ul><ul><ul><ul><li>AB positive or AB negative </li></ul></ul></ul><ul><ul><ul><li>O positive or O negative </li></ul></ul></ul><ul><ul><li>best use is class evidence, often used to rule out suspects </li></ul></ul>
  4. 7. Blood Spatter <ul><li>presumptive test </li></ul><ul><ul><li>preliminary indication as to presence of a particular substance </li></ul></ul><ul><ul><ul><li>may give false positives </li></ul></ul></ul><ul><ul><ul><li>may deteriorate the condition of the evidence </li></ul></ul></ul>
  5. 8. Blood Spatter <ul><li>color tests for blood – </li></ul><ul><ul><li>benzidine test – (not used any more as benzidine found to be a carcinogen) </li></ul></ul><ul><ul><li>Hemastix – designed as a urine dipstick for blood, the strip can be moistened with distilled water and placed in contact with suspected bloodstain, appearance of a green color indicates blood </li></ul></ul>
  6. 9. Blood Spatter <ul><li>color tests for blood – </li></ul><ul><ul><li>Kastle-Meyer test </li></ul></ul><ul><ul><ul><li>when a bloodstain, phenolpthalein, and hydrogen peroxide are mixed, oxidation of the hemoglobin in the blood produces a deep pink color </li></ul></ul></ul><ul><ul><ul><li>not specific to blood – some vegetable materials (potatoes and horseradish for example) will also cause a deep pink color </li></ul></ul></ul>
  7. 10. Blood Spatter <ul><li>Luminol </li></ul><ul><ul><li>reaction of luminol with blood produces light rather than color </li></ul></ul><ul><ul><li>bloodstains will glow a faint blue (luminescence) </li></ul></ul><ul><ul><li>extremely sensitive </li></ul></ul><ul><ul><ul><li>detects bloodstains diluted up to 300,000 times </li></ul></ul></ul><ul><ul><ul><li>may give false positives </li></ul></ul></ul><ul><ul><li>luminol may not interfere with subsequent DNA testing </li></ul></ul>
  8. 12. Blood Spatter <ul><li>location, distribution, appearance of bloodstains and spatters may be useful in interpreting and reconstructing the events that produced the bleeding </li></ul><ul><ul><li>position, shape </li></ul></ul><ul><ul><li>trajectory, origin </li></ul></ul><ul><ul><li>direction </li></ul></ul><ul><ul><li>dropping distance </li></ul></ul><ul><ul><li>angle of impact </li></ul></ul>
  9. 13. Blood Spatter <ul><li>surface texture of location – in general, the harder and less porous the surface, the less spatter </li></ul><ul><li>direction of travel –discerned by stain’s shape </li></ul><ul><ul><li>pointed end of bloodstain always faces its direction of travel </li></ul></ul>
  10. 14. Blood Spatter <ul><li>impact angle of blood on flat surface is determined by degree of circular distortion </li></ul><ul><ul><li>as the angle increases, the stain elongates </li></ul></ul><ul><li>origin of blood spatter in two dimensions can be established through convergence </li></ul><ul><ul><li>drawing straight lines through the long axis of several individual bloodstains </li></ul></ul><ul><ul><li>the intersection (area of convergence) represents origin </li></ul></ul>
  11. 15. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>DNA can be extracted from nucleus of blood cells </li></ul></ul><ul><ul><li>can be analyzed to determine a specific individual or familial relationships </li></ul></ul><ul><ul><li>individualized evidence </li></ul></ul>
  12. 16. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>polymerase chain reaction (PCR) </li></ul></ul><ul><ul><ul><li>small quantities of DNA copied using machine called DNA Thermal Cycler </li></ul></ul></ul><ul><ul><ul><li>each cycle doubles the DNA sample, 30 cycles can multiply DNA a billion-fold </li></ul></ul></ul><ul><ul><ul><li>now DNA can be analyzed by a number of methods </li></ul></ul></ul><ul><ul><ul><li>sample size no longer a limitation in DNA analysis </li></ul></ul></ul>
  13. 18. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>Identification with tandem repeats </li></ul></ul><ul><ul><ul><li>region of a chromosome that contains multiple copies of a core DNA sequence arranged in a repeating fashion </li></ul></ul></ul><ul><ul><ul><li>these tandem repeats account for 30% of the DNA sequence </li></ul></ul></ul><ul><ul><ul><li>used in analysis </li></ul></ul></ul><ul><ul><ul><ul><li>RFLP (Restricted Fragment Length Polymorphism) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>PCR (Polymerase Chain Reaction) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>STR’s (Short Tandem Repeats) </li></ul></ul></ul></ul>
  14. 19. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>RFLP Method </li></ul></ul><ul><ul><ul><li>DNA sample acquired </li></ul></ul></ul><ul><ul><ul><li>treated with restriction enzyme(s) </li></ul></ul></ul><ul><ul><ul><ul><li>cuts DNA sample into fragments of differing sizes (RFLPs) </li></ul></ul></ul></ul><ul><ul><ul><li>electrophoresis </li></ul></ul></ul><ul><ul><ul><ul><li>uses electrical charge to separate RFLPs </li></ul></ul></ul></ul><ul><ul><ul><ul><li>smaller RFLPs move farther than large RFLPs </li></ul></ul></ul></ul>
  15. 20. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>RFLP Method </li></ul></ul><ul><ul><ul><li>hybridization </li></ul></ul></ul><ul><ul><ul><ul><li>fragments transferred to nylon membrane through process called Southern blotting </li></ul></ul></ul></ul><ul><ul><ul><ul><li>nylon sheet treated with radioactive probes containing a complimentary sequence to the RFLPs being identified </li></ul></ul></ul></ul><ul><ul><ul><li>autoradiography </li></ul></ul></ul><ul><ul><ul><ul><li>nylon sheet placed against x-ray film, radioactive decay products strike the film </li></ul></ul></ul></ul><ul><ul><ul><ul><li>length of fragments determined by comparison to control sample </li></ul></ul></ul></ul>
  16. 21. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>RFLP Method </li></ul></ul><ul><ul><ul><li>analysis </li></ul></ul></ul><ul><ul><ul><ul><li>samples that come from the same source will have the same lengths </li></ul></ul></ul></ul><ul><ul><ul><ul><li>so basically, if the samples match in the sets of bands on the developed film, you have a match </li></ul></ul></ul></ul><ul><ul><ul><li>NOTE!!! </li></ul></ul></ul><ul><ul><ul><ul><li>this test alone cannot be used to individualize, tests would be run with different probes </li></ul></ul></ul></ul><ul><ul><ul><ul><li>if all trials (probes) match the same individual you now have “proof” </li></ul></ul></ul></ul>
  17. 22. Blood as an Identification Tool <ul><li>DNA Analysis </li></ul><ul><ul><li>CODIS – Combined DNA Index System </li></ul></ul><ul><ul><ul><li>computer software program </li></ul></ul></ul><ul><ul><ul><li>developed by FBI </li></ul></ul></ul><ul><ul><ul><li>maintains local, state and national databases of DNA profiles from </li></ul></ul></ul><ul><ul><ul><ul><li>convicted offenders </li></ul></ul></ul></ul><ul><ul><ul><ul><li>unsolved crime-scene evidence </li></ul></ul></ul></ul><ul><ul><ul><ul><li>profiles of missing people </li></ul></ul></ul></ul>