Crime Scene Samples

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Crime Scene Samples Reference Samples

• Extract and purify DNA

• Differential extraction in sex assault cases
  separates out DNA from sperm cells

From bioforensics.com
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Method for obtaining DNA
Sterile Omni-swab for obtaining
Cheek cells
Images from http//www.tritechusa.com/kits/images
/FTA20etc/Sterile-Omni-Swab.jpg http//faculty.k
utztown.edu/friehauf/science_outreach/cells.html
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Differential Extraction Only Possible for SPERM

• Vaginal swabs will have a mixture of female fluid
  and semen
• Lyse the epithelial (skin) cells first
• Remove supernatant containing female (epithelial
  cells) portion
• Lyse sperm cells
• From a single exhibit you know have two samples
  for DNA testing

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Differential Extraction of Semen Stain
Mild Detergent and enzyme treatment, rupture all
epithelial cells, leave sperm intact
Male Extract
Modified from bioforensics.com
Graphic from Inman Rudin, An Introduction fo
Forensic DNA Analysis. CRC Press.