Lecture 3 - Forensic DNA Analysis Flashcards
What can change DNA?
Bone marrow transfusion or presence of cancer cells
Why is DNA useful?
That DNA is (mostly) the same no matter what cell type, throughout the person’s life - stable
What sources of DNA are useful in body identification?
Finger/toenails
Body tissue
Bone
Teeth
Why is hair more complicated for DNA profiling?
Hair needs to be pulled from head due to root material needed
What are the types of DNA samples?
Case samples
Reference samples (case specific)
DNA profile databank
Where are DNA case samples taken from?
Crime scene - either taken directly or indirectly, sample taken on swab or tape or directly from fabric
Where are DNA reference samples taken from?
From complainants
From suspects
From other people involved (First responders, ambulance staff, other household members, sexual partners)
Where are DNA in the DNA profile databank taken from?
Criminal Investigations (Bodily Samples) Act 1995
From convicted criminals (permanently held)
From volunteers (can be removed on request)
From people Police intend to charge (temporarily held)
What are the three databanks in DNA Databank Profile Matching?
DNA Profile Databank
Crime Sample Databank
YSTR Crime Sample Databank
What are the profiles in the DNA profile databank from?
Profiles from people
What are the profiles in the crime sample databank from?
Profiles from crimes
What are the profiles in the YSTR crime sample databank from?
YSTR haplotypes from crimes
Why are DNA profiles matched against itself?
To link suspects with previous cases
What does the YSTR technique target?
YSTR technique only targets sample Y DNA in crime scene sample
Why do we have the YSTR crime sample databank?
Useful for SA cases, Y chromosome passed from father to son unchanged, can detect patterns of offending
What is the DNA laboratory process in DNA profiling? (5)
Take a small enough sample to fit into a small tube or beaker
Extract cellular material from substrate and then isolate DNA from cells
Estimate how much total human and male DNA is present
Amplify DNA by making many copies of the areas of interest (PCR)
Separate and detect the profiling results (electrophoresis)
What do the green bars in DNA profile denote?
Green bars denote different areas of DNA we are interested in (locus)
How can we tell if the DNA profile is only from one person?
Only two alleles present, not multiple
How can we determine if a DNA profile is a good quality reference?
Strong peaks
Only two alleles (two peaks)
What body conditions determine DNA sample type?
Fresh - DVI bodies retrieved quickly
Decomposed - die alone
Skeletal - forests or beaches
Burnt
Complete or incomplete - more than one body with pieces mixed together
What body condition is the most challenging to deal with in DNA profiling?
Burnt
Why is DNA not always the best technique in DVI?
DNA profiling requires a specialist laboratory and is slower
(although “Rapid DNA” technologies will change this)
We also need to process reference DNA samples
Why do bones and teeth take longer to be DNA profiled?
They have to be cleaned and ground to powder
What are the two types of reference DNA samples?
Putative samples
Direct family member samples
What are examples of putative reference samples?
Toothbrushes, clothing, other personal items, Guthrie cards
What direct family members are preferred for reference DNA samples and why?
Ideally from parents or from child + partner
If skip generation or siblings, evidence becomes weaker - primary preferred
In what situations is DNA the only option in DVI?
When there are no teeth or dental records - open DVI
When there are no hands/feet or comparison records - or no skin
The DNA Profile Databank and familial searching can help if the body is really unknown
Sometimes the Coroner really wants to be sure about the identification - Circumstantial cases may use DNA to confirm
What are some other considerations when DNA profiling?
Body part - mulitple fragments and whether to test all if too many or too little (either sampled or given to family, not both)
Cross-contamination
Sample from protected areas
Why are internal DNA samples preferred?
Blood from chest cavity is better than a mouth swab due to less cross contamination
Boots protect feet (toenail samples are great.)
What are the DNA sample types for fresh bodies?
Blood from chest cavity
What are the DNA samples types for decomposed bodies?
Finger/toenails
Deep muscle tissue (i.e. psoas)
Bones/teeth (last resort)
What are the DNA sample types for skeletal remains?
Long (weight-bearing) bones
Teeth
(dependant on environment)
