Forensic DNA Profiling:
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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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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


Dr carolyn hancock

Crime Scenes: Types of evidence

BLOOD

WEAPONS

FINGERPRINTS

CIGARETTE BUTT

CLOTHING

BOTTLE

SHOE PRINTS

SEMEN


Dr carolyn hancock

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


Dr carolyn hancock

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


Dr carolyn hancock

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


Dr carolyn hancock

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


Dr carolyn hancock

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


Dr carolyn hancock

Possible outcomes of a DNA result

Suspect 1

Suspect 2

Evidence

Exclusion – no match

Inclusion

Match


Dr carolyn hancock

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


Dr carolyn hancock

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


Dr carolyn hancock

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