Lecture 3 - Forensic DNA Analysis

Question 1

What can change DNA?

Answer 1

Bone marrow transfusion or presence of cancer cells

Question 2

Why is DNA useful?

Answer 2

That DNA is (mostly) the same no matter what cell type, throughout the person’s life - stable

Question 3

What sources of DNA are useful in body identification?

Answer 3

Finger/toenails
Body tissue
Bone
Teeth

Question 4

Why is hair more complicated for DNA profiling?

Answer 4

Hair needs to be pulled from head due to root material needed

Question 5

What are the types of DNA samples?

Answer 5

Case samples
Reference samples (case specific)
DNA profile databank

Question 6

Where are DNA case samples taken from?

Answer 6

Crime scene - either taken directly or indirectly, sample taken on swab or tape or directly from fabric

Question 7

Where are DNA reference samples taken from?

Answer 7

From complainants
From suspects
From other people involved (First responders, ambulance staff, other household members, sexual partners)

Question 8

Where are DNA in the DNA profile databank taken from?

Answer 8

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)

Question 9

What are the three databanks in DNA Databank Profile Matching?

Answer 9

DNA Profile Databank
Crime Sample Databank
YSTR Crime Sample Databank

Question 10

What are the profiles in the DNA profile databank from?

Answer 10

Profiles from people

Question 11

What are the profiles in the crime sample databank from?

Answer 11

Profiles from crimes

Question 12

What are the profiles in the YSTR crime sample databank from?

Answer 12

YSTR haplotypes from crimes

Question 13

Why are DNA profiles matched against itself?

Answer 13

To link suspects with previous cases

Question 14

What does the YSTR technique target?

Answer 14

YSTR technique only targets sample Y DNA in crime scene sample

Question 15

Why do we have the YSTR crime sample databank?

Answer 15

Useful for SA cases, Y chromosome passed from father to son unchanged, can detect patterns of offending

Question 16

What is the DNA laboratory process in DNA profiling? (5)

Answer 16

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)

Question 17

What do the green bars in DNA profile denote?

Answer 17

Green bars denote different areas of DNA we are interested in (locus)

Question 18

How can we tell if the DNA profile is only from one person?

Answer 18

Only two alleles present, not multiple

Question 19

How can we determine if a DNA profile is a good quality reference?

Answer 19

Strong peaks
Only two alleles (two peaks)

Question 20

What body conditions determine DNA sample type?

Answer 20

Fresh - DVI bodies retrieved quickly
Decomposed - die alone
Skeletal - forests or beaches
Burnt
Complete or incomplete - more than one body with pieces mixed together

Question 21

What body condition is the most challenging to deal with in DNA profiling?

Answer 21

Burnt

Question 22

Why is DNA not always the best technique in DVI?

Answer 22

DNA profiling requires a specialist laboratory and is slower
(although “Rapid DNA” technologies will change this)
We also need to process reference DNA samples

Question 23

Why do bones and teeth take longer to be DNA profiled?

Answer 23

They have to be cleaned and ground to powder

Question 24

What are the two types of reference DNA samples?

Answer 24

Putative samples
Direct family member samples

Question 25

What are examples of putative reference samples?

Answer 25

Toothbrushes, clothing, other personal items, Guthrie cards

Question 26

What direct family members are preferred for reference DNA samples and why?

Answer 26

Ideally from parents or from child + partner
If skip generation or siblings, evidence becomes weaker - primary preferred

Question 27

In what situations is DNA the only option in DVI?

Answer 27

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

Question 28

What are some other considerations when DNA profiling?

Answer 28

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

Question 29

Why are internal DNA samples preferred?

Answer 29

Blood from chest cavity is better than a mouth swab due to less cross contamination
Boots protect feet (toenail samples are great.)

Question 30

What are the DNA sample types for fresh bodies?

Answer 30

Blood from chest cavity

Question 31

What are the DNA samples types for decomposed bodies?

Answer 31

Finger/toenails
Deep muscle tissue (i.e. psoas)
Bones/teeth (last resort)

Question 32

What are the DNA sample types for skeletal remains?

Answer 32

Long (weight-bearing) bones
Teeth
(dependant on environment)