DNA Issues: Educating the Jury

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DNA Issues Educating the Jury

• Ronald S. Ostrowski, PhD
• University North Carolina at Charlotte
• rsostrow_at_uncc.edu
• 704-687-4057

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Overview of DNA Technology

• PCR technology
• Capillary electrophoresis
• DNA probes
• Electropherograms

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• Preparation of
• - Discovery items
• - Cross-examination questions
• - Direct examination questions

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Qualifying the Expert

• Prosecutor will attempt to disqualify your
  expert.
• Have you ever been to a crime scene?
• How many forensic DNA samples have you
  analyzed?
• Have you done a differential extraction of a
  forensic vaginal swab sample?

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Connecting with the Jury

• The typical Professor (expert) makes his or her
  living standing up and giving lectures.
• Get the expert out of the witness chair and as
  close to the jury as possible.
• Use visual aids and/or handouts.

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NC v. Benson

• Sexual assault
• Accepted plea bargain

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VA v. Howard

• Sexual assault
• Not guilty verdict

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Acid Phosphatase Test

• AP positive --- State claims evidence for
  presence of semen.

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Gender Analysis(amelogenin)

• AP

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Amelogenin Result
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15 Loci (genes) Tested

• Suspect must be consistent with all loci results
  to be a called a so-called match.

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Selected Issues

• Contamination
• - Accidental transfer of DNA (from environment,
  between samples during preparation, and/or sample
  with amplified product from previous PCR
  reaction).
• Pull up (bleed through)
• - Failure of the analysis to discriminate
  between dye colors leading to spurious peaks.

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Selected Issues (cont.)

• Allelic Drop Out
• - Detection of only one of two alleles at a
  locus.
• Degradation
• - Breakdown of alleles-with the potential for
  misinterpretation.
• Mixed Samples
• - Samples containing DNA from two or more
  individuals.

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Selected Issues (cont.)

• Population Genetics
• - Inappropriate application of formulae
• Validation
• Process demonstrating that the lab procedures are
  reliable and robust and executed correctly by lab
  personnel.
• Certification
• - Successful inspection or audit by an outside
  accrediting agency.

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Selected Readings

• Forensic DNA Typing. Butler, J.M. Academic
  Press. 2001.
• Evaluating Forensic DNA Evidence. Thompson,
  W.C., Ford, S., Doom, T., Raymer, M., and Krane,
  D.E. The Champion. April 2003.