6A Forensics Flashcards
how to determine T.O.D
- body temp
- extent of rigor mortis
- level of decomposition
- entomology
- stages of succession of insects
after what period of time is body temp no longer useful?
24 hours
what conditions affect rate of cooling of body?
- body size -> bigger bodies have SMALL s.a : vol = slower
- body position -> bunched up = slower
- clothing -> clothes = slower (traps heat)
- air movement -> no air = slower (movement takes heat energy away)
- humidity -> more = slower (like mummies in Egypt)
- temp of surroundings -> higher = slower (mummies)
- water = faster (takes heat energy away)
rigor mortis
stiffening of muscles and joints after death
how does muscle size affect rigor mortis?
small muscles stiffen FIRST and unstuffed LAST
why does rigor mortis occur?
- muscles run out of ATP -> actin and myosin (muscle fibres) stick together
- muscles unstiffen when muscle fibres start to break down
no O₂ = anaerobic = makes lactic acid = lowers pH = DENATURES enzymes that make ATP
if body is WARM and NOT STIFF how long ago since death?
no more than 3 hours
if body is WARM and STIFF how long ago since death?
3-8 hours
if body is COLD and STIFF how long ago since death?
8-36 hours
if body is COLD and NOT STIFF how long ago since death?
> 36 hours
autolysis
breakdown of body tissues using body’s own ENZYMES from dig system and lysosomes
what happens after autolysis?
bacteria from gut invade TISSUES and release MORE ENZYMES
-> usually in ANAEROBIC CONDITIONS so favours anaerobic bacteria
what happens in first 36 hours of decomposition?
greenish colour in abdomen
what happens in 36-72 hours of decomposition?
- greenish colour spreads to rest of body
- abdomen darkens to reddish green
what happens in after 72 hours of decomposition?
- discolouration darkens to purple black
what happens one week after decomposition?
gas/liquid blisters appear eg. H₂SO₄, CO₂
gases from respiring organisms that break it down eg. bacteria
what happens more than one week after decomposition?
gas released and body DEFLATES
how does heat affect autolysis?
autolysis …
increased by mild heat
decreased by intense heat
how does humidity affect autolysis?
dry conditions = slow autolysis and can stop it in some conditions
vice versa
forensic entomology
study of insects and their relation to a criminal investigation
how can insects in dead body affect T.O.D?
- age of maggots determined by LENGTH and area they are found in and using LIFE CYCLE
- some maggots taken to lab -> grow them and note how long to pupate -> so deduce age
how to identify body?
- fingerprints
- dental records
- identity papers
- GENETIC FINGERPRINT (DNA profile)
what is purpose of electrophoresis?
separate DNA fragments to use for DNA fingerprinting
describe gel electrophoresis (after PCR)
- DNA placed in well in gel and covered in buffer solution (conducts electricity)
- electrical current passed through gel -> DNA fragment is -vely charged = move towards anode at far end of gel
- short DNA fragments = move FASTER and travel FURTHER through gel -> so DNA fragments separated according to LENGTH
what is polymerase chain reaction (PCR)?
technique used to create many copies of DNA segment
describe PCR
(used to amplify DNA)
reaction mixture made …
- DNA sample
- free nucleotides
- primers
- DNA polymerase
- mixture heated to 95 °C -> breaks H-bonds between 2 strands of DNA
- mixture cooled to between 50 - 65 °C -> so primer can bind to strands
- mixture heated to 72 °C -> so DNA polymerase can work
- DNA polymerase lines up free DNA nucleotides alongside each template strand = complementary strands
- 2 new copies of fragment of DNA made and ONE CYCLE PCR COMPLETE
- cycle starts again -> all 4 strands used as templates
-
each PCR DOUBLES amount of DNA
eg. 1st cycle 2 x 2 = 4 DNA fragments
2nd cycle 4 x 2 = 8 etc
primers
short pieces of DNA that are COMPLEMENTARY to bases at START of fragment
DNA polymerase
enzyme that CREATES new DNA strands
satellites
repeated DNA seq within introns
a.k.a variable number tandem repeats
DNA profile
fingerprint of organisms DNA
unique to you
used to identify people and determine genetic relationships
