DNA profiling

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  • DNA Profiling
    • process
      • 1. Sample collection
        • crime scene
          • swab
            • freeze
          • double swabbing (wet/dry)
            • submit both to lab - doubles the amount of DNA
          • mini taping
        • evidence clothing
          • 0.5cm x 0.5cm
          • cellular
        • control DNA samples
          • buccal scrape
      • 2. DNA extraction
        • separates DNA from other source
          • several methods
            • organic extraction
              • phenol-chloroform
            • chelex extraction
              • 5% chelex beads
            • qiagen extraction
              • spin column technology
      • 3. DNA quantification (optional)
        • optimum quantity is less than 1 nanograms
          • techniques
            • 260nm absorbance
            • ethidium-broide plate fluorescence
            • slot-blot procedure
            • SYBR green
      • 4. PCR amplification
        • allows short stretch of DNA to be amplified
          • samples are heated to 94C to denature (seperate the single strands) the target DNA
            • temp lowered to allow the left and right primers to anneal (base pair) to their complementary sequences. the primers are designed to bracket the DNA region to be amplified.
              • temp raised to 72C which allows the polymerase to bind to each primed site and extend a new DNA strand
                • procedure repeats
                  • 1 strand turns to 2 - 2 strands turn to 4 - 4 strands turn to 8 etc
      • 5. capillary electrophoresis - seperate out
        • separation according to size
          • small molecules travel fastest
      • 6. electropherogram analysis - graph
        • male - two peaks
        • female - one peak
    • PED
      • Police Elimination Database
      • any police professional is entered on to it
    • NDNAD
      • National DNA Database
        • owned by NCA - national crime agency
      • DNA profiles stored onto NDNAD
        • adults - convicted - indefinite
        • adults - arrested but not convicted - 6 years
        • under 18 - convicted of a serious offence or more than one minor offence - indefinite
        • under 18 - single minor offence - 5 years
        • 16 & 17 - arrested but not convicted - 6 years
        • all other under 18 - arrested but not convicted - 3 years
    • what is it?
      • polymerase chain reaction - photocopy DNA
      • uses STR (short tandem repeats)
      • reduction in analysis time
    • crime scene samples
      • single hair
      • fingerprints
      • single blood spot
      • fingernail scrapings
    • DNA inheritance
      • inherited from parents
        • relatives are more likely to have similar characteristics of DNA
      • two possibilities
        • sibling of offender
        • parent or child of offender
      • basic principles
        • twenty alleles
          • ten from mother and ten from father
        • very expensive
        • has been used to convict
          • close matches
    • mtDNA
      • mitochondrial DNA
        • from mother
          • cannot distinguish individual
            • no nucleus present
      • used for skeletal remains
    • Y-STR analysis
      • y chromosome only (males)
      • used in sexual offences cases and paternity cases
      • high number of markers needed

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