forensic dna analysis genome 475 05/04/2015. forensics “of, relating to, or denoting the...
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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
Screening 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
http://www.wildlife-photography.uk.com/blog/?p=7033
Jeffreys et al. 1985
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
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
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 of locus is robust High 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
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/)
X
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Forensic DNA Typing, 2005
Summary of TechniquesTest type Comments
RFLP Requires larger amounts of DNA (micrograms).
DNA must be undegraded.
PCR 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
Next generation sequencing New era arriving in forensic DNA analysis
COmbined DNA Index System(CODIS)
Examines 13 STRs The National DNA Index (NDIS) contains:
>11,685,829 offender profiles,
1,944,423 arrestee profiles
619,280 forensic profiles
CODIS 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
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