Forensics - biological evidence

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  • Created by: Ashlee
  • Created on: 30-04-15 14:15
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  • Biological evidence
    • visual identification
      • texture/colour
      • enhancing
        • strong light source
        • UV light
        • laser
        • fixed wavelength light source
    • blood
      • bright red - changes to brown/dark green
      • plasma = hormones, waste, antibodies
        • 55% of volume
        • when fibrinogen removed it is serum
      • platelets
        • helps blood clot
      • red blood cells
        • haemoglobin carries oxygen
        • contains blood type antigens
      • white blood cells
        • fight infection - part of immune system
      • at scene
        • presumptive tests
          • Kastle Meyer Test (KM)
            • ethanol, phenolphthalein and hydrogen peroxide on swab
              • turns pink if positive
          • Hemastix
          • Leucomalachite green (LMG)
            • reagent of zinc, leucomalachite green, water and glacial acetic acid
              • add to hydrogen peroxide
                • if turns blue/green = positive
          • oxidation reactions
          • false positives
          • cheap and quick but further tests required
    • semen
      • pale and crusty
      • suspension of spermatazoa cells
      • slightly acidic
      • rich in calcium, zinc, sodium and citric acid
      • DNA in head of sperm
      • presumptive tests
        • lab based
        • microscopy
          • to see sperm cells
        • acid phosphate test
          • acid phosphatase secreted by prostate gland
            • if semen present, when mixed with dye and sodium it will turn blue/green/orange/red (depending on dye)
        • UV light
          • flourescent
    • saliva
      • fluid excreted by salivary glands
      • mucin - lubricates food
      • salivary amylase - digestive starch
      • can contain skin cells from inside mouth
      • presumptive tests
        • none at scene
        • starch test
          • add iodine if turns blue/black it is positive
    • blood stain pattern analysis
      • the interpretation of dispersion, shape, volume, number and relationship of bloodstains to reconstruct events
      • active blood stains
        • cast off
        • movement
        • body (artery/cough)
        • gun shot/high velocity
      • passive blood stains
        • force of gravity
        • formation of outer ring
      • transfer bloodstains
        • direct contact with contaminated objects
        • objects leave silhuette/pattern
        • footwear/fingermark
      • contact/collapse phase - blood is pushed outwards into a rim
      • angles important
    • properties of blood
      • viscosity = 3-4 mP.s-1
      • surface tension = 0.058 N.m-1
      • density = 1060 kg/m3

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