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Dr. Carolyn Hancock

Forensic DNA Profiling: An introduction to scientific principles. Dr. Carolyn Hancock. Presentation to the Portfolio Committee of Police Criminal Law (Forensic Procedures) Amendment Bill B9-2013. Crime Scenes: Types of evidence. BLOOD. WEAPONS. FINGERPRINTS. CIGARETTE BUTT. CLOTHING.

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Dr. Carolyn Hancock

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  1. Forensic DNA Profiling: An introduction to scientific principles Dr. Carolyn Hancock Presentation to the Portfolio Committee of Police Criminal Law (Forensic Procedures) Amendment Bill B9-2013

  2. Crime Scenes: Types of evidence BLOOD WEAPONS FINGERPRINTS CIGARETTE BUTT CLOTHING BOTTLE SHOE PRINTS SEMEN

  3. Useful characteristics of DNA • Everyone has a unique DNA profile (except identical twins) • DNA in every cell of an individual is identical • An individual’s DNA profile remains unchanged throughout life Fighting crime with science

  4. DNA in crime scene investigation Because the DNA of all people is different we can: • Identify or exclude a suspect • Identify missing persons Fighting crime with science

  5. Body fluids used in DNA profiling Cells Body fluids containing DNA saliva sample blood Each body cell: contains 46 chromosomes Chromosomes sample semen Each chromosome: contains one DNA molecule sample

  6. DNA 5% functional genes 95% non functional DNA 46 chromosomes DNA is double stranded 4 different molecules for building blocks (A, C, G and T) C A T A G C A C A G T T G C G T Sequences are specific for functional genes Too little variation to be useful for DNA profiling Non functional DNA: High proportion of sequence variation Enough differences to make DNA of each person unique Used for DNA profiling

  7. DNA profiling: How it works Chr 11 ATCT ATCT ATCT ATCT ATCT ATCT ATCT Chr 11 ATCT ATCT ATCT ATCT ATCT Region (locus) on Chromosome 11 with repeated segments – referred to as microsatellite - STR Extract DNA out of sample and amplify DNA segments Separate and visualize DNA fragments in conducting gel Store profile as Numbers 5/7 Longer molecule – 7 repeats Shorter molecule – 5 repeats Digital Profile Machine Profile

  8. Possible outcomes of a DNA result Suspect 1 Suspect 2 Evidence Exclusion – no match Inclusion Match

  9. Reference Profile Analysis Buccal swab Sample Collection STR Typing at laboratory Male: 13-13; 14-15; 16-12; 13-10; 13-15; 16-16 Profile entered onto relevant index on DNA Database REFERENCE SAMPLE DESTRUCTION

  10. Information stored on DNA Database • A DNA profile is stored on the Database as a list of letters and numbers These numbers are not associated with any physical trait, genetic disease or human behavioral pattern • Only personal information: sex • Case number, sample bar code, laboratory number

  11. Privacy issues

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