6. Immunity, infection and forensics
6.a Forensics
Estimating time of death
Body temperature
● When metabolic processes are taking place, the human body has an internal
temperature of 37℃. From the TOD, metabolic processes slow down and eventually
stop, this causes body temp. to fall until it is in equilibrium with its surroundings (algor
mortis).
● Human bodies cool at a rate of around 1.5-2℃ per hour.
● Conditions such as air temperature, clothing, position and body weight can affect the
cooling rate.
Rigor mortis
● Rigor mortis if the stiffening/contraction of muscles.
● When the body is dead, muscle cells become deprived of oxygen, this causes
anaerobic respiration to take place in cells. This results in a buildup of lactic acid in
the muscle.
● The pH of the cell decreases (due to rise in lactic acid), inhibiting ATP producing
enzymes. No ATP means bonds between myosin and actin become fixed and the
body stiffens.
1. 2-6 hours - eyelids, jaw and small muscles stiffen
2. 8-11 hours - centre of body stiffens
3. 12 hours - complete rigor (entire body stiffens)
4. 15-36 hours - slow loss of rigor, small muscles in head and neck first
5. 36-48 hours - rigor disappears, muscles become relaxed
Forensic entomology
● Forensic entomology is the study of the colonisation of insects on a body
● A dead body provides an ideal habitat for many species of insects, different insect
species will colonise a body at different times after death, providing information about
the TOD.
- Flies will be found on the body within a few hours after death, while beetles
will only colonise the body later
● Another clue that insects can provide is the stage of life cycle they are at
- E.g. blowfly eggs will hatch after about 24 hours so if larvae are present on
the body it indicates that the person died more than 24 hours ago
● Other insects have longer life cycles, so if only blowfly larvae are
found it indicates that only 24 hours has passed since TOD
- Factors that might affect the progression of insect life cycles include
● Drugs that may be present in the body
● Humidity of the surrounding
● Oxygen availability
● Temperature
, 6. Immunity, infection and forensics
Decomposition
● Immediately after death bacteria and enzymes begin to decompose the body
1. Hours to a few days
● Cells and tissues are being broken down by body’s own enzymes and
bacteria
● Skin begins to turn green
2. Few days to few weeks
● Decomposition of tissues and organs
● Gases produced causing bloating
● Skin begins to blister and fall off
3. Few weeks
● Tissues begin to liquefy and seep out into surrounding areas
4. Few months to few years
● Only a skeleton remains
5. Decades to centuries
● Skeleton begins to disintegrate
Succession
● The types of organism found in a dead body change over time, this is called
succession
1. Immediately after death, the conditions are most favourable for bacteria
2. As bacteria decomposes tissues, conditions become favorable for flies and
their larvae
3. When fly larvae feed on a dead body they make conditions favourable for
beetles
4. As the body dries out, flies leave and beetles remain as they decompose dry
tissue
5. When no tissues remain, most organisms leave
DNA profiling
Obtaining a DNA profile
● A DNA profile is a genetic fingerprint
● How a DNA profile is made:
1. Sample of DNA obtained
2. PCR machine is used to amplify the DNA
3. A fluorescent tag or stain is added to the DNA fragments
4. Gel electrophoresis is used to separate the DNA
5. The gel is then viewed under UV light
Polymerase chain reaction (PCR)
● A polymerase chain reaction is used to make millions of copies of specific regions of
the DNA through which it is amplified and fragmented
1. Denaturation
● DNA is heated to 95℃
● Hydrogen bonds break
6.a Forensics
Estimating time of death
Body temperature
● When metabolic processes are taking place, the human body has an internal
temperature of 37℃. From the TOD, metabolic processes slow down and eventually
stop, this causes body temp. to fall until it is in equilibrium with its surroundings (algor
mortis).
● Human bodies cool at a rate of around 1.5-2℃ per hour.
● Conditions such as air temperature, clothing, position and body weight can affect the
cooling rate.
Rigor mortis
● Rigor mortis if the stiffening/contraction of muscles.
● When the body is dead, muscle cells become deprived of oxygen, this causes
anaerobic respiration to take place in cells. This results in a buildup of lactic acid in
the muscle.
● The pH of the cell decreases (due to rise in lactic acid), inhibiting ATP producing
enzymes. No ATP means bonds between myosin and actin become fixed and the
body stiffens.
1. 2-6 hours - eyelids, jaw and small muscles stiffen
2. 8-11 hours - centre of body stiffens
3. 12 hours - complete rigor (entire body stiffens)
4. 15-36 hours - slow loss of rigor, small muscles in head and neck first
5. 36-48 hours - rigor disappears, muscles become relaxed
Forensic entomology
● Forensic entomology is the study of the colonisation of insects on a body
● A dead body provides an ideal habitat for many species of insects, different insect
species will colonise a body at different times after death, providing information about
the TOD.
- Flies will be found on the body within a few hours after death, while beetles
will only colonise the body later
● Another clue that insects can provide is the stage of life cycle they are at
- E.g. blowfly eggs will hatch after about 24 hours so if larvae are present on
the body it indicates that the person died more than 24 hours ago
● Other insects have longer life cycles, so if only blowfly larvae are
found it indicates that only 24 hours has passed since TOD
- Factors that might affect the progression of insect life cycles include
● Drugs that may be present in the body
● Humidity of the surrounding
● Oxygen availability
● Temperature
, 6. Immunity, infection and forensics
Decomposition
● Immediately after death bacteria and enzymes begin to decompose the body
1. Hours to a few days
● Cells and tissues are being broken down by body’s own enzymes and
bacteria
● Skin begins to turn green
2. Few days to few weeks
● Decomposition of tissues and organs
● Gases produced causing bloating
● Skin begins to blister and fall off
3. Few weeks
● Tissues begin to liquefy and seep out into surrounding areas
4. Few months to few years
● Only a skeleton remains
5. Decades to centuries
● Skeleton begins to disintegrate
Succession
● The types of organism found in a dead body change over time, this is called
succession
1. Immediately after death, the conditions are most favourable for bacteria
2. As bacteria decomposes tissues, conditions become favorable for flies and
their larvae
3. When fly larvae feed on a dead body they make conditions favourable for
beetles
4. As the body dries out, flies leave and beetles remain as they decompose dry
tissue
5. When no tissues remain, most organisms leave
DNA profiling
Obtaining a DNA profile
● A DNA profile is a genetic fingerprint
● How a DNA profile is made:
1. Sample of DNA obtained
2. PCR machine is used to amplify the DNA
3. A fluorescent tag or stain is added to the DNA fragments
4. Gel electrophoresis is used to separate the DNA
5. The gel is then viewed under UV light
Polymerase chain reaction (PCR)
● A polymerase chain reaction is used to make millions of copies of specific regions of
the DNA through which it is amplified and fragmented
1. Denaturation
● DNA is heated to 95℃
● Hydrogen bonds break
