Fundamentals of Forensic DNA Typing

Slides prepared by John M. Butler

June 2009

Chapter 18Future Trends

Chapter 18 – Future Trends

Chapter SummaryAs the power of forensic DNA typing has been demonstrated over the past two decades, there has been an accelerated growth to the field both in terms of depth and breadth. National DNA databases in the UK and US now number in the millions of samples and are actively used to solve crimes without suspects. While the standard set of STR markers in use will not likely change in the immediate future, techniques and genetic markers capable of extracting more information from a sample will continue to be developed. Trends in human identity testing will likely include the need for more characterized and validated genetic markers to aid application to more complex kinship analysis. Continued growth can be expected for the foreseeable future in this dynamic and important application of modern DNA science.

Core set of markers(e.g., CODIS 13 STRs)

Past and Present

Future

(a)

(b)

(c)

(d)

Possible scenarios for extending sets of genetic markers to be used in national DNA databases

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Loci Described

Use in Casework

Court Presentation/ Acceptance

Internal Validation

ResearchGovernment

Funded or Private

Development

Typically by Commercial Manufacturer

ForensicApplicationForensic Labs

Assay Constructed

Population Study

Information GatheredReleased to Community

Kit Developed

Kit Tested

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Primary Steps in Adopting New Genetic Markers

Lower amounts of DNA being

tested

Challengingkinship search

questionsStandard

STR Typing (DNA Profile)

Core Competency

Sufficient DNA quantity (ng)

Direct Matching (or Parentage)

Solution: Replicate Testing

Solution: Additional Markers (Y-chromosome, more STRs) and

Multiple Reference Samples

Touch DNA Attempts (poor quality, mixtures, low-level

stochastic effects)

Familial Searching Attempts (fishing for brothers or other relatives)

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Lower amounts of DNA being

tested

Challengingkinship search

questionsStandard

STR Typing (DNA Profile)

Core Competency

Sufficient DNA quantity (ng)

Direct Matching (or Parentage)

Solution: Replicate Testing

Solution: Additional Markers (Y-chromosome, more STRs) and

Multiple Reference Samples

Touch DNA Attempts (poor quality, mixtures, low-level

stochastic effects)

Familial Searching Attempts (fishing for brothers or other relatives)

Going Beyond the Core Competencies of Forensic DNA Testing

Be very cautious when outside the box…

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Problems of Sibling Searches

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K(database)

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Mother’s alleles

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A “Crystal Ball” to the Future?

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The FutureThe Past The Present

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500 – 25,000 bp 100 - 500 bp 50 - 150 bp

Lab Automation

• Robotics• LIMS• Expert Systems

Unique Challenges with Adopting New Technologies by Forensic DNA Laboratories

• Validation

• Limited funding for capital equipment

• Need for court acceptance (Frye and Daubert)

Unique Challenges to Forensic DNA Testing

• High quality results needed (every time) because of impact on individual’s liberty

• Regulated environment– Proficiency testing of analysts– Accreditation of labs– Auditing to National Quality Assurance Standards

• Care to prevent contamination• The ever present politics and bureaucracy that

exists in many government labs

Additional Challenges• Multiplex STR amplification require a fairly narrow

amount of input DNA to product high quality results

• High-throughput needs for databanking labs– Automated software for data review

• An attitude of being (and needing to be) “error-free”

• Separating biological fluids – perpetrator’s sperm from victim’s vaginal epithelial cells

• Mixture components can be difficult to decipher

General Predictions for the Future

• Refer to The Future of Forensic DNA (NIJ 2000)

• STRs will play a major role for the foreseeable future due to large sizes of existing and rapidly growing DNA databases

http://www.ojp.usdoj.gov/nij/pubs-sum/183697.htm

•Report published in Nov 2000

•Asked to estimate where DNA testing would be 2, 5, and 10 years into the future

Conclusions

STR typing is here to stay for a few years because of DNA databases that have grown to contain millions of profiles

Principles of Forensic DNA for Officers of the Court

1. Introduction

2. Biology of DNA

3. Practical Issues Specific to DNA Evidence

4. Forensic DNA Laboratory

5. Assuring Quality in DNA Testing

6. Understanding a Forensic DNA Lab Report

7. Statistics and Population Genetics

8. Mitochondrial DNA & Y-STR Analysis

9. Forensic DNA Databases

10.Collection of DNA Evidence

11.Pretrial DNA Evidence Issues

12.Victim Issues

13.Trial Presentation

14.Postconviction DNA Cases

15.Emerging Trends

http://www.dna.gov/training/otc/

Content of Section 15 “Emerging Trends” from Officers of the Court

• Topic 1 :: Single Nucleotide Polymorphisms (SNPs) • Topic 2 :: Automation

– Microarrays (Chip Technology)– Portable DNA Typing Laboratory – Low Copy Number DNA Analysis

• Topic 3 :: Microbial Forensics and DNA Testing • Topic 4 :: Other Non-human Forensic DNA Analysis • Topic 5 :: DNA Typing and Physical Appearance

– Biogeographical Ancestry – Approximate Age Determination

http://www.dna.gov/training/otc/

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The Future• More Robotics

• Expert Systems

• Animal & Plant DNA

• Physical Characteristics

• Ethnicity Estimation

Time Line Showing the Potential for DNA Deposition/Transfer

Time

Crime Event

Opportunity for DNA Transfer from Perpetrator

Opportunity for Adventitious Transfer

Adapted from Gill, P. (2002) BioTechniques 32(2): 366-385, Figure 5

Potential to “Contaminate”

Discovery

Investigators arrive, detect, and recover evidentiary material

Laboratory analysis

Analysis completed

Higher sensitivity techniques are most likely to pick up

previously deposited (background) DNA

Conclusions

• This is an exciting time to be involved in forensic DNA testing

• However, it is a little scary because technology is advancing so rapidly on some fronts

• Thus, training for both the scientific and legal communities is vital to make the most effective use of the wonderful power of DNA technology

Improvements in Forensic DNA Analysis

• Biology– Improved DNA extraction with automation– New capabilities for recovery of information from

degraded DNA samples (e.g., miniSTRs)

• Technology– Parallel processing of DNA with capillary arrays– Expert systems for automated data interpretation

• Genetics– Ethnicity estimations (with STRs and/or SNPs)– Larger Y-STR and mtDNA population databases

Effective Training is Needed in All Areas

Training Materials Available or Planned• DNA Basics• Validation• STR Analysis and Capillary Electrophoresis• Y-Chromosome Analysis• Mitochondrial DNA Analysis• Expert Systems• Low-Copy Number (LCN) DNA Testing• Statistics• Mixture Interpretation

http://www.cstl.nist.gov/biotech/strbase/training.htm

Training Materials and Review Articles• Workshops on STRs and CE (ABI 310/3100)

– Taught with Bruce McCord (Florida Int. Univ.)– NEAFS (Sept 29-30, 2004)– U. Albany DNA Academy (June 13-14, 2005)– AAFS Feb 2006 Workshop #6 (February 20, 2006)

• Other Workshops– Validation (August 24-26, 2005)– mtDNA Analysis (March 13-15, 2006)– Expert Systems (March 27, 2006)

• PowerPoint Slides from Forensic DNA Typing, 2nd Edition– >150 slides available now (~1,000 planned) for download– http://www.cstl.nist.gov/biotech/strbase/FDT2e.htm

• Review Articles– ABI 310 and 3100 chemistry – Electrophoresis 2004, 25, 1397-1412

– Core STR Loci – J. Forensic Sci. 2006, 51(2): 253-265

http://www.cstl.nist.gov/biotech/strbase/training.htm

Chapter 18 – Points for Discussion

• What are some potential advantages to microchip CE devices?

• Why are allelic ladders unnecessary with mass spectrometry techniques for STR analysis?

• Why are forensic laboratories typically slow to adopt new technologies?