current issues in forensic dna profiling
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Current Issues in Forensic DNA Profiling. Dan E. Krane Biological Sciences, Wright State University Dayton, OH 45435-0001. Why might two DNA profiles “match”?. • A suspect left material at the scene of a crime. - PowerPoint PPT PresentationTRANSCRIPT
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Current Issues in Forensic DNA Profiling
Dan E. KraneBiological Sciences, Wright State UniversityDayton, OH 45435-0001
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The business of DNA profiling:
Roughly 900,000 felony convictions per year in US
DNA profiles generated primarily for sexual offenses, murder and assaults.
Combined DNA Index System (CODIS)
Less than 1% of DNA profiles reviewed by defense experts
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DNA contents of biological samples:Type of sample Amount of DNA
Hair:
Blood 30,000 ng/mLstain 1 cm in area 200 ngstain 1 mm in area 2 ng
Semen 250,000 ng/mLpostcoital vaginal swab 0 - 3,000 ng
plucked 1 - 750 ng/hairshed 1 - 12 ng/hair
Saliva 5,000 ng/mLUrine 1 - 20 ng/mL
22
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DNA profiling approaches:
VNTRs
PCR/reverse dot blots
STRs
Advantages Disadvantagesresolving power,inexpensive
testing time,sensitivity,data comparisons
sensitivity,testing time,data comparisons
resolving power,mixtures
very sensitive,testing time,data comparisons,resolving power
start-up costs
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Why might two DNA profiles “match”?
• A suspect left material at the scene of a crime.
• A suspect coincidentally has the same DNA profile as someone who really was at the crime scene.
• The laboratory declaring the “match” is in error.
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Allele 2
Allele 7
Allele 12
Allele 13
Allele 17
Primer bindingsite
Tandemlyrepeated
sequences
Amplified region
Short Tandem Repeats (STRs)
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Additional considerations with STR testing:
• Extremely sensitive.
• Mixture interpretations are challenging.
What does a DNA profile mean?
Where did a DNA profile come from?
How old is the DNA in a DNA profile?
• Amplification variability.
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Profile is clearly a mixture of at least two individuals (but this is a database profile from the MN BCA).
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Additional considerations with STR testing:
• Extremely sensitive.
• Mixture interpretations are challenging.
What does a DNA profile mean?
Where did a DNA profile come from?
How old is the DNA in a DNA profile?
• Amplification variability.
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3-person mixture that has no more than 4 alleles at every locus.
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Additional considerations with STR testing:
• Extremely sensitive.
• Mixture interpretations are challenging.
What does a DNA profile mean?
Where did a DNA profile come from?
How old is the DNA in a DNA profile?
• Amplification variability.
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Amplifications from same dilution tube (~60 pg).Allelic imbalance present.“Different DNA profiles” @ THO1 and CSF1P0.
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Amplifications from same dilution tube (~30 pg).Allelic imbalance present. Allele dropout @ D18.“Different DNA profiles” @ D3, D21, D18 and D13.
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Amplifications from 2 different dilution tubes (~1 ng and ~125 pg).Allelic imbalance present.“Different DNA profiles” @ D16, TPOX, CSF1P0 and D7.
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A forensic lab assigned the major/minor alleles incorrectly @ THO1:major profile=6,6 and minor profile=8,9.3. Correct call is major profile=6,8 and minor profile=6,9.3 of 2-person mixture, 3:1 ratio.
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A forensic lab assigned the major/minor alleles incorrectly @ FGA:major profile=22,22 and minor profile=21,23. Correct call is major profile=22,23 and minor profile=21,22 of 2-person mixture, 3:1 ratio.
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What you see when you open a CD provided in discovery:
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What you see when you try to open the files on a discovery CD:
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An electropherogram using the software’s default settings:
GenoTyper Graph
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What the testing lab provides is not always the same as the default electropherogram:
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Genophiler Zoom
• Genophiler also provides a zoomed graph to 150 RFU’s• Shows smaller peaks more clearly• Here, the peaks that were disregarded by the lab may be evidence of an unknown, minor contributor to the sample
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Genophiler output:
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Genophiler also flags potential problems for further review:
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Project Screen Button
• Screen shot of GeneScan
• Shows exactly what samples were added and what parameter files were used for the analysis
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Analysis Parameters Buttons
• See exactly what analysis settings were used
• Parameter files also copied to CD
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Finding Problems With Samples: Raw Data
Good raw data begins with a large peak followed by smaller peaks
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• Bad raw data is indicated by wildly uneven peaks• Indicates lab analysis problems
Finding Problems With Samples: Raw Data
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Finding Problems With Samples: EPT Data
• Shows current, voltage, laser power, and temperature• For good analysis, should be constant (flat)
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Finding Problems With Samples: EPT Data
• Problem EPT data is not flat• Indicates problems with lab analysis
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Genophiler Report
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Genophiler Report, continued
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Automation Process
• Select samples and settings in one screen
• Analysis can be performed unattended
• Unlimited analysis runs can be set up at one time
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Forensic BioInformatic Services
• Uses Genophiler to generate easily interpreted files
• Objectively applies analysis parameters to all samples
• Fast turn around times
• Efficiently draws attention to problems requiring further review
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Acknowledgements:
Genophiler support: Dr. Travis Doom Dr. Mike Raymer Carrie Rowland Jason R. Gilder
STR experts: Dr. Bill Thompson Dr. Simon Ford Dr. Dan Krane
Support:Wright State University, Dayton, OH
Forensic BioInformatic Services; 2850 Presidential Drive, Suite 150, Fairborn, OH, 45324; phone: (937) 426-9270; web site: BioForensics.com