Recovering DNA

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  • Recovering DNA
    • Identification of biological evidence
      • Locating biological material is necessary before appropriate collection
        • Presumptive Tests - test which can establish the possibility that a specific bodily tissue/fluid is present
        • Confirmatory Tests - tests which can identify a specific biological material
        • Appropriate collection
          • Prevent contamination
            • PPE
        • Appropriate Packaging
          • Prevent contaminaion
            • Swabs, brown paper bags, tubes, wet/dry, frozen/ambient
    • Types of biological material from a crime scene
      • Semen
        • A thick fluid containing sperm and other secretions from the male reproductive system
        • The positive identification of semen can be extremely important in sexual abuse cases
        • Presumptive Tests
          • Alternative Light Source (ALS), Seminal Acid Phosphate Test (SAP)
        • Confirmatory Tests
          • Visualisation of sperm following staining, Lateral flow strips, mRNA analysis and PSA
      • Blood
        • Composed of red and white cells suspended in a liquid matrix called plasma.
        • Generally visible to the naked eye but may not be clear against dark surface and if cleaning has been attempted.
      • Salvia
        • The fluid released when the mouth waters that plays an important role in both mechanical and chemical digestion
        • Presumptive Tests
          • Alternative Light Source and the Starch Iodine Test
        • Confirmatory Test
          • Lateral Flow Strips and mRNA analysis
    • Degradation of DNA Samples
      • Forensic samples usually show degradation
        • More cellular material is required to produce a DNA profile
          • Sometimes it is not possible to produce a DNA profile
      • In practice 15 or more cells are required to generate consistently good-quality DNA profiles from fresh material


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