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

Crime Scenes: Types of evidence BLOOD WEAPONSFINGERPRINTS CIGARETTE BUTT BOTTLE CLOTHING SHOE PRINTS SEMEN

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 Useful characteristics of DNA Fighting crime with science

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

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

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

DNA profiling: How it works 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 ATCT Chr 11 Region (locus) on Chromosome 11 with repeated segments – referred to as microsatellite - STR Machine Profile

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

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

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

Privacy issues