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DNA - A Prosecutor’s Practice Notebook Inventory


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Photo examples of degradation environments including a snowy mountain terrain, fire pit, an insect, a water pond, a broken leg lying on a dirt ground
National Institute of Justice (NIJ) (see reuse policy).

The defense may argue that the DNA typing result is unreliable because the evidence sample was exposed to heat or environmental insults prior to typing. First, the DNA analyst should explain that even if the evidence were exposed, this would not render the typing unreliable. Exposure could:

  1. Degrade the evidence to the degree that no DNA profile at all could be obtained
  2. Degrade the evidence so that the results at some but not all loci were inconclusive (a partial DNA profile)
  3. Have no appreciable effect on the DNA sample, with a full DNA profile being obtained despite some degradation occurring

The DNA analyst should also explain that none of these would render the typing results unreliable.

Second, the DNA analyst should explain that in no case would degradation spontaneously create a profile which matches the defendant's DNA. Third, the DNA analyst should describe that degradation does not transform one person's DNA into the DNA of someone else.

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