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Things that can muck up a DNA Profile

Things that can muck up a DNA Profile

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Things that can muck up a DNA Profile

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  1. The list is long and distinguished. . . Things that can muck up a DNA Profile By Christine Funk, with a lot of help from her friends. . . Board of Public Defense Trial Team 651.539.4846

  2. There are many, many ways to muck up a DNA profile • Collection Muck Ups -Contamination during collection • Interpretation Muck Ups – Mixed Samples • Amplification Muck Ups • Degradation • Primer Binding Muck Ups - Peak Height Imbalance • Capillary Muck Ups - Blobs and Noise • Dye Muck Ups - Pull Up • Spikes • DNA Mutation Muck Ups - Tri-allelic Patterns; Off Ladder Alleles • Machine Muck Ups - Signal Data • Low Level DNA - Allelic Imbalance • Interpretation Muck ups – Examiner Bias • Math Muck Ups – Fun with Numbers!

  3. Let’s have a giggle, shall we?

  4. Collection Muck Ups:Typically, DNA in criminal cases has done a little traveling. . .

  5. Primary Transfer Picture courtesy of Jennifer Friedman

  6. Secondary transfer Clipping courtesy of Bob Blaiser

  7. Collection muck up

  8. The Leskie Decision “ 8. . .The match to the bib occurred as a result of contamination in the laboratory and was not an adventitious match. . ."

  9. The Leskie Decision “ 8. . . The samples from the two cases were examined by the same scientist within a close time frame."

  10. Mixture Interpretation • How does one interpret a mixture, that is, which bands or peaks are alleles and which are artifacts or errors?

  11. Sample Mixture ExampleProfiler Plus data 4 peaks at a single locus Higher than expected stutter FGA D3S1358 VWA blue panel Amel green panel Relative Fluorescence Units D8S1179 D21S11 D18S51 “Stutter” on wrong side of allele Imbalance in X and Y peak ratios D13S317 yellow panel D5S818 D7S820

  12. Who’s in the Mix? Care to take a guess?

  13. Who’s in here? • XY 11, 15 28, 30 12, 15

  14. But wait! What if… • XY 11, 15 28, 30 12, 15 • XY 13, 15 32.2, 32.2 17, 19

  15. Whoops! I meant to say… • XY 11, 15 28, 30 12, 15 • XY 13, 15 32.2, 32.2 17, 19 • XY 11, 13 28, 32.2 12, 17

  16. Perspective is everything

  17. Alleles Present: 13, 17, 18

  18. Alleles Present: 13, 17, 18 Possible Contributors to D3: 13, 13; 13, 17; 13,18;17, 17; 17,18; 18,18 SIX possible profiles in D3

  19. But Wait!! There’s more. . . *ladders not to scale

  20. Alleles Present: 16, 17, 18, 19

  21. Alleles Present: 16, 17, 18, 19 Still MORE contributors: 18, 18; 18, 19; 19, 19 Possible Contributors: 16, 16; 16, 17; 16, 18; 16, 19; 17, 17; 17, 18; 17, 19

  22. 10!! • 10 Possible Profiles in vWA!!!

  23. 6 profiles from D3 10 profiles from vWA 60 profiles so far. We have 14 loci to go. . .

  24. Why this is hard: • You don’t know how many people are in the mix • You don’t know when and where their alleles overlap • You don’t know if you have alleles that have dropped out due to low copy numbers • You don’t know if you have a triallelic pattern or stutter or primer binding site mutation

  25. Amplification Muck up

  26. 6.3% 6.2% 5.4% STR Alleles with Stutter Products DNA Size (bp) D8S1179 D21S11 D18S51 Allele Relative Fluorescence Units Stutter Product

  27. Stutter in Pictures – First, let’s review how it’s supposed to happen. . . G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  28. Stutter in Pictures – how amplification is supposed to happen G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  29. Stutter in Pictures: amplification as it should be. . . G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 1 2 2 3 3 4 4

  30. Stutter in Pictures – Amplification gone horribly awry. . . G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  31. Stutter in Pictures G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  32. Stutter in Pictures G T C T G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  33. Stutter in Pictures G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  34. Stutter in Pictures G T C T G T C T G T C T C A G A C A G A C A G A C A G A 1 2 3 4

  35. Stutter in Pictures G T C T G T C T G T C T C A G A C A G A C A G A C A G A C A G A C A G A C A G A G T C T G T C T G T C T G T C T 1 1 2 2 3 3 4 4

  36. Stutter in Pictures G T C T G T C T G T C T C A G A C A G A C A G A C A G A C A G A C A G A C A G A G T C T G T C T G T C T G T C T 1 1 2 2 3 3 4 4

  37. St… St… Stutter!!

  38. Stutter Happens So does teeny tiny contribution

  39. Pop Quiz • Why do we care about stutter?

  40. A funny thing happened on the way to the forum. . .

  41. Degradation Ahem. DNA degradation.

  42. Degradation

  43. Things that are insulting to DNA

  44. Degradation: I know it when I see it!

  45. Bonus points: • How could increasingly smaller DNA sample size be a problem in a criminal case?

  46. When degradation isn’t degradation

  47. What causes inhibition? Hint: Monty Pyton wouldn’t know. . .