Expert Systems forExpert Systems forAutomated STR AnalysisAutomated STR Analysis

SWGDAMSWGDAMQuantico, VAQuantico, VA

Mark W. PerlinMark W. PerlinJanuary, 2003January, 2003

DNA Is Clue to 1971 Murder: A recent, random test links a state prison inmate to the old El Dorado case. January 10, 2003

DNA Clue Cracks Open Unsolved 1979 Slaying: Colorado felon charged in San Pablo girl's death. December 4, 2002

S.F. Transient Held in Rapes of Homeless Women: DNA match led to suspect. October 19, 2002

DNA links felon to rape: The arrest marks the 100th match in state database. August 23, 2002

DNA links parolee to old rape case: Database helps authorities score 'cold hit' on suspect in attack. August 21, 2002

DNA yields arrest warrant in 1978 killing. August 14, 2002

The analyst will simply submit the items for DNA analysis, using the final data interpretation step to determine relevance to the ongoing investigation ... The bottleneck becomes the interpretation of analytical results and the technical review process. ... Although these processes are currently dependent upon manual applications, software solutions are emerging that can be integrated into an automated approach.

Collect Crime Scene EvidenceCollect Crime Scene Evidence

Generate DNA DataGenerate DNA Data

Review DataReview Data

Present Results to Legal SystemPresent Results to Legal System

Collect Crime Scene EvidenceCollect Crime Scene Evidence

Generate DNA DataGenerate DNA Data

Review DNA DataReview DNA Data

Present Results to Legal SystemPresent Results to Legal System

TrueAllele™TrueAllele™

datadata

data peaksdata peakssize + [DNA]size + [DNA]

modelmodel

1. Input data

2. Q/C gel run

3. Call alleles

4. Output result

FSS ABI/377 ValidationFSS ABI/377 ValidationResourcesResources• • Data: 22,000 genotypes (SGMplus)Data: 22,000 genotypes (SGMplus)• • People: 6 reviewers + 6 managers People: 6 reviewers + 6 managers • • Time: 8 weeks work + 4 weeks reportTime: 8 weeks work + 4 weeks report

ComponentsComponents• • Peak height correlation (GS vs TA)Peak height correlation (GS vs TA)• • Establish baseline height (error-free)Establish baseline height (error-free)• • Designation accuracy (human vs TA)Designation accuracy (human vs TA)• • Network/computer environmentNetwork/computer environment• • QMS documentationQMS documentation

ResultsResults• • Greater yield with TAGreater yield with TA• • No errors on quality dataNo errors on quality data

denialdenial

angeranger

bargainingbargaining

depressiondepression

acceptanceacceptance

Generate STR DataGenerate STR Data

UK National DNA DatabaseUK National DNA Database

Person reviewsPerson reviewsa fractiona fraction

of the dataof the data

TrueAllele expert systemTrueAllele expert systemscores all STR data and scores all STR data and assesses data qualityassesses data quality

Validation MethodValidation Method

1. Obtain original data1. Obtain original data2. Process data in TrueAllele™ ES2. Process data in TrueAllele™ ES (auto-setup, process run, Q/A, (auto-setup, process run, Q/A, call alleles, apply rules, check)call alleles, apply rules, check) computer: accept/reject/editcomputer: accept/reject/edit3. Review all data3. Review all data one person, many computersone person, many computers human: accept/reject/edithuman: accept/reject/edit4. Generate results & stats4. Generate results & stats

Validation ResultsValidation Results

Computer: ~85% data, no review needed Computer: ~85% data, no review needed Human: Designations are correctHuman: Designations are correct

TrueAllele expert system can eliminateTrueAllele expert system can eliminatemost human review of STR DNA datamost human review of STR DNA data

JustAllele™JustAllele™

Genotype ProbabilityGenotype ProbabilitySample @ D7S820Sample @ D7S820

Option 1Option 1

Option 2Option 2

99% Confidence Allele Set =99% Confidence Allele Set = { { 10, 1110, 11 } } Database SearchingDatabase Searching

DNA Mixture ModelDNA Mixture ModelLinear Mixture AnalysisLinear Mixture Analysis

M.W. Perlin and B. Szabady, M.W. Perlin and B. Szabady, ““Linear mixture analysis: Linear mixture analysis: a mathematical approach to resolving mixed DNA samples,a mathematical approach to resolving mixed DNA samples,””

Journal of Forensic SciencesJournal of Forensic Sciences, November, 2001., November, 2001.

d = G x w d = G x w + e+ e

The Contributor ProblemThe Contributor Problem

DATADATAsample profilessample profiles

GENOTYPESGENOTYPESof of

contributorscontributors

WEIGHTSWEIGHTSof of

contributorscontributorsin samplesin samples

contributorscontributors

One SampleOne Sample

Sample C:Sample C:Unknown (A) 70%Unknown (A) 70%Unknown (G) 30%Unknown (G) 30%

1 ng DNA1 ng DNAPowerPlex16PowerPlex16

ABI/310ABI/310

samplesample

con

trib

uto

rsco

ntr

ibu

tors

Two SamplesTwo Samples

Sample A: Reference Sample A: Reference &&

Sample C:Sample C:Reference (A) 70%Reference (A) 70%Unknown (G) 30%Unknown (G) 30%

1 ng DNA1 ng DNAPowerPlex16PowerPlex16

ABI/310ABI/310

samplessamples

con

trib

uto

rsco

ntr

ibu

tors

Three SamplesThree Samples

Sample D:Sample D:(A) 50%(A) 50%(G) 50%(G) 50%

1, 1/2, 1/4, 1/8 ng DNA1, 1/2, 1/4, 1/8 ng DNAPowerPlex16PowerPlex16

ABI/310ABI/310

Sample C:Sample C:(A) 70%(A) 70%(G) 30%(G) 30%

Sample E:Sample E:(A) 30%(A) 30%(G) 70%(G) 70%

Two Contributors, No ReferenceTwo Contributors, No Reference

samplessamples

con

trib

uto

rsco

ntr

ibu

tors

samplessamples

con

trib

uto

rsco

ntr

ibu

tors

1 ng1 ng

1/8 ng1/8 ng

Collect Crime Scene EvidenceCollect Crime Scene Evidence

Generate DNA DataGenerate DNA Data

Review DNA DataReview DNA Data

Present Results to Legal SystemPresent Results to Legal System

The analyst will simply submit the items for DNA analysis, using the final data interpretation step to determine relevance to the ongoing investigation ... The bottleneck becomes the interpretation of analytical results and the technical review process. ... Although these processes are currently dependent upon manual applications, software solutions are emerging that can be integrated into an automated approach.