M5 Flashcards
Methods used to ID human remains
- Facial characteristics
- Scars, marks, & other special body features
- Dental matching
- Fingerprint comparison
DNA profiles from human remains can be essential in:
- Missing person investigations
- Unidentified Remains Identification
- Mass disaster identification
If a reference sample is available, follows same underlying workflow of regular DNA profile as follows:
- Generate DNA profile from unknown evidentiary sample & known reference sample, or enter into CODIS
- Followed by comparison of the 2
- Inclusion/Exclusion/Incomplete
Generating DNA profiles from skeletonized/decomposed human remains is
challenging
NamUS
National Missing and Unidentified Person System
What happens do DNA after death?
- DNA begins to degrade
- Cell death occurs
- Cell membranes rupture & release enzymes that degrade cellular structures
- Chemical reactions to modify & break the DNA strands
- Followed by microbes, both within & external to the body
- DNA degradation occurs over time
DNA begins to degrade
immediately after the cells die
Cell death occurs once a cell is no longer in
contact w/the body’s circulating oxygen supply
Cell membranes rupture & release enzymes that
degrade cellular structures
Chemical reaction act to
modify & break the DNA strands
DNA degradation occurs over time as hydrolytic & oxidative chemical reactions damage the molecules by
fragmentation & chemical modification.
DNA persists in bones & teeth longer than
soft tissues because of rigid structure (provides protection).
DNA binds to
hydroxyapatite of the hard tissues - stabilizes the DNA
Molecular taphonomy is the study of the
various intrinsic & extrinsic factors that influence the degradation of the body’s molecular structures (e.g., DNA).
- Environmental Factors
Differential preservation in different skeletons, in different bones, within the
same skeleton, & even variations in DNA quality & yield across the same bone.
Depositional environment plays a greater role in
degradation than the absolute age.
Bone type & density
contributes to perservation
Different Environmental Factors are
- Temperatures
- Moisture levels
- Oxygen levels
- Microorganism Activity
- Soil Composition
- pH
- Bone Type
Temperature
Autolysis occurs at a maximum chemical activity at
34 degrees C to 40 degrees C
* Two-fold to three-fold increase 10 degree C
Temperature influences microbial activity in that
warmer temp increases activity, thus cooler temps will favor DNA preservation
Some circumstances where mild heating (during extraction) may be beneficial as it makes the
bone brittle, releasing out the DNA.
- Moisture *
Water molecules participate in hydrolytic reactions that
fragment and modify DNA
- Moisture *
The more water/humidity, the more
DNA damage
- Moisture *
Some circumstances where water may influence other environmental variables; for example
peat bog, creates low oxygen environmental and burial in salt water reduce microbial activity.