6A Forensics

Question 1

Factors determining TOD

Answer 1

Core body temperature/ algor mortis- usually 37 degrees, decreases around 2 degrees an hour until ambient temperature
Degree of rigor mortis- after 4 hours, starting in the head + smaller muscles
Forensic Entomology- the study of insect colonisation and looking at life cycle stages
Extent of decomposition- bacteria begin decomposition of the body immediately
Stage of succession- the types of organism found in the body as conditions are made more favorable to them

Question 2

Core body temperature in TOD

Answer 2

After death, the body’s metabolic processes slow down and eventually stop, meaning heat energy isnt produced and bod temperature falls until it reaches ambient temperature

rate of cooling affected by environmental temperature, clothing and body weight

Question 3

Rigor mortis

Answer 3

Muscle cells begin to be deprived of oxygen so respire anaerobically.
lactic acid is produced which lowers the pH of the cells and inhibits ATP producing enzymes
no ATP means myosin and actin bonds become fixed and the body stiffens

Starts 4 hour wears off around 24h

affected by the degree of muscle development and temperature

Question 4

Forensic entomology

Answer 4

Studying the type of insects that are present on the body and the stage of the life cycle which organisms are in
Conditions such as drugs humidity oxygen and temperature will affect life cycles

Question 5

decomposition and TOD

Answer 5

Bacteria and enzymes begin to decompose the body
Hours- days: Greenish colour skin
Days- weeks Microorganisms decompose tissues, producing gases causing bloating and blistering
Weeks: Tissues liquefy and seep out
Months- years: skeleton

affected by temperature, oxygen availability

Question 6

Stages of succession

Answer 6

Bacteria-> flies+ larvae-> beetles-> noone

affected by location of the body eg under/above ground or in water

Question 7

Polymerase chain reaction (PCR)

Answer 7

Mixture containing DNA sample, free DNA nucleotides, primers and DNA polymerase heated to 95 to break hydrogen bonds
cooled to 60 to allow primers to anneal to the strands
Heated to 72 so DNA polymerase can line up free nucleotides alongside each template strand using complementary base pairing.

Question 8

Making a DNA profile

Answer 8

PCR to amplify sample
Fluorescent tag added to DAN
Gel electrophoresis
View under UV light
Compare profiles: more similar = closer genetic relation
thickness + width of band, distance travelled, pattern overall

Question 9

Gel electrophoresis

Answer 9

Separates DNA fragments based on their length
Agarose gel with wells in a gel tray-> gel tank The wells should be at the cathode
\buffer solution covers gel
Using micropipette add loading dye to samples and add DNA to wells, under buffer. Use a clean micropipette tip each time.
Pass current through the gel for 30 minutes
Remove buffer