Cybergenetics © 2007-2014 1
Revolutionising DNA analysis in major crime investigations
The Investigator Conferences Green Park Conference Centre
May, 2014 Aylesbury, Buckinghamshire
Mark W Perlin, PhD, MD, PhD Cybergenetics, Pittsburgh, PA
Cybergenetics © 2003-2014
Commonwealth v. Lyons homicide: DNA mixture evidence
Victim's blood spatter pulsating spray from
severed carotid artery
75% victim 25% other
Cybergenetics © 2007-2014 2
DNA molecule
Copy DNA
Copy intact DNA
Normal DNA signal
Cybergenetics © 2007-2014 3
Degraded DNA
Can’t copy broken DNA
Longer molecules copy less With degradation, a longer DNA molecule has a greater chance of having a break
DNA decay curve
DNA size
Obs
erve
d D
NA
With degradation, a longer DNA molecule makes fewer DNA copies
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Degraded DNA signal
Degraded DNA Mixture
Degraded other DNA
Victim DNA
Match statistic comparison
Human Computer
42,000 9,500,000,000,000
Cybergenetics © 2007-2014 5
Computer Interpretation of Quantitative DNA Evidence
Commonwealth v. Lyons June, 2011
Reading, PA
Mark W Perlin, PhD, MD, PhD Cybergenetics, Pittsburgh, PA
Cybergenetics © 2003-2011
DNA evidence interpretation Evidence
item Evidence
data Lab Infer
10 11 12
Evidence genotype
Known genotype
10, 12 @ 50% 11, 12 @ 30% 12, 12 @ 20%
10, 12
Compare
Computers can use all the data Quantitative peak heights at locus D8S1179
victim
other
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People may use less of the data
Over threshold, peaks become allele events.
Under threshold, alleles vanish.
All-or-none allele peaks; ignore victim genotype
Threshold
How the computer thinks Consider every possible genotype solution
victim other
Explain the peak pattern Better explanation
gives a higher probability
Evidence genotypes victim other
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DNA match information
Probability(evidence match) Probability(coincidental match)
How much more does the suspect match the evidence than a random person?
6x
Is the suspect in the evidence? A match between the suspect and the evidence
is 9.46 trillion times more probable than coincidence.
Yes, with a reasonable degree of scientific certainty, evidence item Q9 contains DNA
from the genotype of suspect item K2.
Is the victim in the evidence? A match between the victim and the evidence
is 1.27 quintillion times more probable than coincidence.
Yes, with a reasonable degree of scientific certainty, evidence item Q9 contains DNA
from the genotype of victim item K1.
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