Forensic DNA Analysis
Genome 475
05/04/2015
Forensics
“Of, relating to, or denoting the application of
scientific methods and techniques to the
investigation of crime”
http://www.oxforddictionaries.com/
First biological testing in crime


Part of forensic
serology
1900: Karl
Landsteiner described
the ABO blood groups
RBC
phenotype
Reaction
with Anti-A
Reaction
with Anti-B
O
-
-
A
+
-
B
-
+
AB
+
+
Landsteiner et al. 1900
Forensic Processing Workflow
Collection
of
evidence
Screenin
g for
blood,
semen,
saliva,
etc.
DNA
extraction
Quantitation
of DNA
Amplification
of DNA
Analysis
of DNA
Generation of
Result
DNA Collection

From crime scene items

Blood, seminal fluid, saliva,
epithelial cells, and faeces

Cigarette butts, drinking
vessels, bite marks, masks,
door handles, steering wheels,
knife handles, hair follicles

Reference sample: blood,
buccal swabs, pulled hairs
An Introduction to Forensic Genetics 2011
Discovery of
minisatellites

Alec Jeffreys (1985)

Studying seal
myoglobin and
discovered the first
minisatellite

Human myoglobin
gene
Jeffreys et al. 1985
http://www.wildlife-photography.uk.com/blog/?p=7033
Minisatellites




Prone to be in subtelomeric regions of chromosomes
Have core repeat sequence (6 to 100 bp)
Alleles range from 1 kb to 20 kb
Result in multiple alleles
Restriction Fragment Length
Polymorphism (RFLP)
DNA
CS
DNA
fingerprinting
GGGCAGGAXG
S1
S2
Detection of low amounts of DNA

Invention of PCR by Kary Mullis (1983)

Amplification of small quantities of DNA

Focus on microsatellites (short tandem repeats)
Short tandem repeats (STRs)
Throughout the genome
 Core unit between 1 and 6 bp
 Alleles from 50 to 300 bp
 Those used in forensic genetics are
tetranucleotide repeats (4)

An Introduction to Forensic Genetics 2011
STR analysis
PCR
Dye signal
Capillary
Electrophoresis
36
56
Size (nt)
Short tandem repeat output


Output for each STR
is the repeat count
Easy for storage in
databases
STR
Repeats
1
10,12
2
8,13
3
7,9
4
8,8
5
13,14
6
12,15
7
7,6
Short tandem repeats (STRs)

Selection criteria for forensics
 Discrete
and distinguishable alleles
 Amplification
 High
of locus is robust
power of discrimination
 Absence
of genetic linkage with other loci
being analyzed
 Low
levels of artifact during amplification
 Ability
to be amplified as part of multiplex PCR
Potential Problems
Outcomes of DNA Result

Exclusion (Non-match): Genotype
profiles of suspect and crime scene are
different

Inconclusive: Genotype profiles can not
rule out suspect.

Match (inclusion): Genotype profiles of
suspect and crime scene are exactly the
same. Statistical significance is
assigned to this by a match probability.
(http://strbase.org/)
Forensic DNA Typing, 2005
Summary of Techniques
Test type
Comments
RFLP


PCR





Next generation sequencing

Requires larger amounts of
DNA (micrograms).
DNA must be undegraded.
Requires smaller amounts of
DNA than RFLP
Can be somewhat degraded
Extremely sensitive to
contamination at crime scene
and in crime lab
More prone to error than
RFLP
Most often used now due to
speed and sensitivity
New era arriving in forensic
DNA analysis
COmbined DNA Index System
(CODIS)

Examines 13 STRs

The National DNA Index (NDIS) contains:
 >11,685,829
 1,944,423
 619,280
 CODIS
offender profiles,
arrestee profiles
forensic profiles
has produced over 280,451 hits
assisting in more than 267,461 investigations.
Profile Applications

Missing persons investigations

Anastasia Romanov –
daughter of Tsar Nicholas

All of family except her and her
brother were found in a grave

Thought to be missing

Ultimately her and her brother’s
remains were discovered in
another grave
biography.com
Profile Applications

Mass disasters

9/11

As of March 2015: Of
2,753 people reported
missing in the attack,
remains of 1,113 have
never been found
www.nationalgeographic.com
Profile Applications

Paternity

Eddie Murphy and
Mel B
First crime solved using DNA forensics
Aronson et al. 2005
First crime solved using DNA forensics

1983: Rape and murder of
a 15-year old girl (Lydia
Mann) in Leicestershire

1986: Nearly identical case
in nearby town (Dawn
Ashworth)

Police focused on a young
kitchen porter with low IQ
who ultimately confessed
to the second crime
DNA from crime scene did
not match the kitchen
porter DNA
Aronson et al. 2005
First crime solved using DNA forensics

~5,000 men subjected to
testing


Blood groups
DNA profiling

Colin Pitchfork avoided
the mandatory testing

1987: He was ultimately
discovered and
convicted of both crimes
First crime to exonerate
one person and incriminate
another using DNA profiling
Aronson et al. 2005
Current Efforts

Innocence
projecthttp://www.innocenceproject.org/

As of 4/27/2015
 DNA
exonerations: 329
 Average
number of years served: 14
 Number
of real perpetrators found: 140
Current Efforts
www.innocenceproject.org/