1. Collecting DNA Evidence

2. Most common – blood and semen
If exposed to environment – risk of DNA breakdown and contamination
Keep bio evidence on original surface, if possible
If not, swab surface for evidence, plus comparative samples

3. If exposed to envir., cell can open and degrade DNA – hard to gain good evidence
RFLP Analysis – sensitive to degradation, but still may give useful DNA profile
Likely to degrade if exposed to certain enzymes or microorganisms
Warm, moist environs increase chance of exposure

4. Need to remove moisture – dry and freeze sample ASAP
Take item with bio evid (or swab) directly to lab

5. Collecting Biological Evidence at a Crime Scene
No bare hands; no sneezing or coughing near evidence
Clean gloves for each piece of evidence
Package separately
Air dry objects with wet evidence
Dry evidence in paper bag or envelope

6. Cotton swab and water if cannot remove piece of evidence
Reference samples – known for comparison
Taken from suspects, victims, family members

7. Presumptive Tests At crime scene For blood –
- Luminol – sprayed on large area; needs darkness to see glow
* picks up blood even if diluted 10 million X
* doesn’t destroy DNA

8. 50% + of DNA cases involve sexual assault
For semen –
- Chemicals and fluorescent dyes to see seminal fluid
- look for acid phosphatase
- Kits test for prostate-specific antigen (PSA)
- Microscope to detect sperm

9. For saliva – test for amylase (breaks down starch)
- Phadebas reagent – starch w/ dye; when reagent & amylase mix, dye is released
- Starch iodine test – turns blue

10. Mitochondrial Analysis
Circular DNA in mitochondria (mtDNA)
Only inherited from mother
Many copies per cell
Less degradation
Not unique – same for all of a mother’s children
Useful in missing persons and mass disasters

11. Mostly from teeth, hair, bones (femur)
Extracted to separate from PCR inhibitors
Can spare bones and teeth for physical exam
Hair sample destroyed, so examined first, then extracted

12. Y-Chromosome Analysis
Inherited father to son
Can match a father, brother, or paternal relative
Useful in sexual assault, missing persons, genealogy
Not individual evidence, but useful if little DNA left