dr. carolyn hancock forensic dna profiling: an introduction to scientific principles presentation to...
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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
BLOODWEAPONSFINGERPRINTS
CIGARETTE BUTT BOTTLECLOTHING
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
Each chromosome:contains one DNA molecule
ChromosomesChromosomes
CellsCells
Each body cell:contains 46 chromosomes
Each body cell:contains 46 chromosomes
salivasaliva
bloodblood
semensemen
Body fluids containing DNABody fluids containing DNA
samplesample
samplesample
samplesample
46 chromosomes46 chromosomes
5% functional genes5% functional genes
95% non functional DNA95% non functional DNA
DNA
Used for DNA profiling
Non functional DNA:High proportion of sequence variationEnough differences to make DNA of each person unique
Non functional DNA:High proportion of sequence variationEnough differences to make DNA of each person unique
AA TTGGCCAA CC CC AA
4 different molecules for building blocks (A, C, G and T)4 different molecules for building blocks (A, C, G and T)
Sequences are specific for functional genesToo little variation to be useful for DNA profiling
Sequences are specific for functional genesToo little variation to be useful for DNA profiling
TT TT GG GG GG TTAACC
DNA is double stranded 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 repeatsLonger molecule – 7 repeats
Shorter molecule – 5 repeatsShorter molecule – 5 repeats
DigitalProfile
DigitalProfile
ATCTATCT ATCTATCT ATCTATCT ATCTATCT ATCTATCT ATCTATCT ATCTATCT
ATCTATCT ATCTATCT ATCTATCT ATCTATCT ATCTATCT
Chr 11
Chr 11
Region (locus) on Chromosome 11 with repeated segments – referred to as microsatellite - STR Region (locus) on Chromosome 11 with repeated segments – referred to as microsatellite - STR
Machine Profile
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; 16-16Profile 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
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