Topic 6A- Forensics Flashcards
(19 cards)
When microorganisms such are bacteria/fungi decompose organic matter so it can be respired, what is respired out and what does this feed back into?
Carbon dioxide and methane are respired out into the atmosphere. This feeds back into the carbon cycle.
Name the five factors which must be taken into consideration when measuring the time of death.
Body temperature
Degree of muscle contraction
Forensic entomology
Extent of decomposition
Stage of succession
What is Algor Mortis?
Why does this occur?
Where the body cools down after death, until it reaches the ambient temperature (temperature of the surroundings).
Simply, the body has died and is no longer undergoing metabolic processes such as respiration, so the heat released from such processes is no longer being released.
What is the rate of cooling of the body after death?
Between 1.5-2.0 degrees per hour
What affects body cooling?
The temperature of the air in the surroundings
The body weight (more fat will mean more insulation, so slower cooling)
Any clothing worn (clothes act as insulators, so the rate of cooling will be slowed down.)
When does muscle contraction begin after death?
What is rigor mortis?
4-6 hours after death.
The process in which the muscles in the body begin to contract after death, causing the body to stiffen (due to a lack of oxygen)
Why does oxygen deprivation cause the muscles to contract?
Anaerobic respiration occurs, so lactic acid is produced. This lowers the pH, and inhibits enzymes which produce ATP (ATP synthase/ATPase), so ATP isn’t produced. This means the bonds between actin and myosin (actin-myosin crossbridge) isn’t broken, and the it becomes stiff.
In which order does the muscles in the body begin to contract?
The smallest muscles in the body contract first (i.e. the ones in the head), and the most developed largest muscles in the lower body contract last. This is because rigor mortis is affected by the degree of muscle development, as well as temperature (higher temperatures allow chemical reactions to occur faster in the body)
What is forensic entomology?
Studying which insects have colonised the body to estimate the time of death
Which animals tend to colonise the body first, and at what time is this?
Flies, just hours after the death.
Flies lay eggs to hatch what?
Which tend to hatch after how long?
Bowfly larvae
The lifecycle of bowfly larvae eggs is 24 hours. So if the eggs are present but aren’t hatched, the body can’t have been dead for more than 24 hours.
What conditions affect the life cycles of insects?
Oxygen availability
Temperature
Humidity
Drugs
Extend of decomposition:
Hours to days
Days to weeks
Weeks to months
Months to years
Decades to centuries
Cells and tissues are digested by bacteria and enzymes present in the body. This is PUTREFACTION, where the skin will turn a green ish colour.
Tissues and organs are decomposed by microorganisms. These microorganisms are decomposing organic matter which are releasing gases like carbon dioxide and methane. This means the body will bloat. As the body becomes more acidic so enzymes regulating the structure of skin will not be working and pressure builds up, the skin will begin to deteriorate, blister and fall off.
The body’s cells and tissues and organs are liquified at this point, and this seeps out of the body.
The only thing left is the skeleton, after tissues and organs have been liquified post decomposition and have seeped out of the body.
The skeleton will disintegrate
Stages of succession have been established due to the conditions of the body after death. Explain the stages of succession:
Initially, conditions are favourable for bacteria (as the pH hasn’t changed much). The bacteria will decompose the tissues.
This makes the environment favourable to flies and their larvae.
When the flies feed on the body, the conditions become favourable to beetles, so they move in.
As the body begins to dry out, the conditions are no longer favourable to flies, so they leave, and the beetles remain to decompose the dry tissue.
After all the tissues have been decomposed, the environment is not favourable to most organisms.
What is the difference between succession in animals and plants?
In animals, they can stay and continue decomposition whilst other animals come in and colonise the body. In plants, the animals must not remain and almost take their turn.
What is DNA profiling?
A “genetic fingerprint”
It is a method to help to identify any genetic relationships between humans, animals, or plants.
Explain PCR
Make a master sample containing the DNA sample, free complementary nucleotides, primers and DNA polymerase.
Heat to 95 degrees to break the hydrogen bonds holding the dna strand together to seperate into two template strands.
Then cool to 55-65 degrees to allow the primers to ANNEAL to the template strands.
Then heat to 72 degrees to allow the DNA polymerase to bind and line up complementary free nucleotides to the template strand, forming phosphodiester bonds between the nucleotides. This will have created 2 identical copies of the DNA.
Repeat this cycle around 29 times, to gather enough DNA to make a DNA profile. Add a fluorescent tag to all DNA fragments to make them viewable in solution.
Devise and Explain gel electrophoresis.
Pour agarose gel into a gel tray, with a well mold. Allow this to solidify, and place the gel into a gel box.
Pour buffer solution into the reservoirs around the gel allowing the buffer to reach over the gel.
Then place a known volume of DNA into each well, with the same volume of loading dye to ensure the dns sample sinks to the bottom as the is will ensure the most efficient transport of the dna across the gel.
Do this using a micropipette.
Place lid over the gel box and then place wires onto each side. Allow the current to flow through and allow to run for 30 mins.
Then view under UV light, analyse bands to determine the genetic similarities between the DNA from the different individuals.
Why is DNA profiling useful?
It can identify genetic relationships between humans, animals, and plants.
Useful for things like paternity testing.
Can identify whether animals are genetically similar, and can therefore allow things such as captive breeding programmes to avoid inbreeding, to avoid reducing the number of alleles in the gene pool, and increase genetic diversity by breeding the individuals which are the least closely related.
