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

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

Restriction Fragment Length Polymorphism (RFLP)

DNACS S1 S2

GGGCAGGAXG

DNA fingerprinting

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

36 56

Dye

sig

nal

Size (nt)

Capillary Electrophoresis

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

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/)

X

?

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

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/