Forensics - TOD Flashcards
What are 5 factors that help estimate the time of death?
- Body temperature
- Degree of muscle contraction
- Forensic entomology
- Extent of decomposition
- Stage of succession
What are the regular patterns of decay?
fresh - bloated - decaying - dry
What is forensic entomology?
- when somebody dies, the body is quickly colonised by a variety of different insects.
TOD can be estimated by idenitifying the type of insect present on the body.
1st : flies are the first to appear usulally a few hours after death. beetles colonise at a later stage
2nd: blowfly larvae hatch from eggs about 24hrs after they are laid. If only blowfly eggs are found, TOD was no more than 24hrs ago.
What is the affect of temperature on a insects life cycle?
the higher the temperature, the faster the metabolic rate and the shorter the life cycle.
How can the degree of muscle contraction help estimate the TOD?
About 4-6 hrs after death, the muscles in a dead body start to contract and become stiff - (rigor mortis)
- rigor mortis begins when muscle cells become deprived of oxygen
- respiration still takes place in the muscle cells, but its anaerobic which causes a build up of lactic acid in the muscle.
- The PH of the cells decreases due to the lactic acid, inhibiting enzymes that produce ATP.
- No ATP = bonds between myosin and actin are fixed = body stiffens
What is the extent of decomposition ?
Hours - a few days
Cells and tissues are being broken down by the body’s own enzymes and bacteria that were present before death. The skin beings to turn a greenish colour.
What is the extent of decomposition?
A few days - a few weeks
Microorganisms decompose tissues and organs. This produces gases which cause the body to become bloated.
What is the extent of decomposition?
A few weeks
Tissues begin to liquefy and seep out into the area around the body.
What is the extent of decomposition?
A few months - a few years
only skeleton remains
Explain the role of microorganisms in decomposition?
Fungi & bacteria use enzymes to hydrolyse dead organic matter into smaller molecules that they can use as respiratory substrates.
- releases CO2 and methane
What is DNA profiling and how is it used?
A DNA profile is a fingerprint of an organisms DNA used to determine genetic relationships between humans, animals and plants.
How can DNA fragments be amplified in vitro?
PCR - polymerase chain reaction
What is PCR used for?
- used to make lots of copies of specific regions of the DNA in just a few hours.
In PCR, what does the reaction mixture contain?
DNA sample, free nucleotides, primers and DNA polymerase.
primers - short pieces of DNA that are complementary to the bases at the start of the fragment you want.
Describe the process of PCR.
- A reaction micture is set up
- The DNA mixture is heated to 95 degrees to break the hydrogen bonds between the two strands of DNA.
- The mixture is then cooled to 50 - 65 degrees so that the primers can bind (anneal) to the strands.
- The reactin mixture is heated to 72 degrees so DNA polymerase can work.
- The DNA polymerase lines up free DNA nucletides alongside each template strand. Complementary base pairing means new complementary strands are formed.
- Two new copies of the fragment of DNA are fromed and one cycle of PCR is complete.
- cycle starts again and this time all 4 strands are used as templates.
- amount of DNA = 2^ n
