Lecture 5 - Forensic DNA profiling Flashcards
Why is DNA useful?
Most cells contain nuclear DNA.
DNA in the nucleus, this DNA is usually the same in every cell
That DNA is (mostly) the same no matter what cell type, throughout the person’s life
Forensic scientists only look at the areas of DNA that we know to be different between people.
They do not do whole genome sequencing, do very specific areas of different chromosomes that they know to be very different person to person and this helps them to distinguish the DNA profile of one person from another person
We can compare a DNA profile from a crime scene sample with the DNA profile of a specific person (or a database of profiles) and make an assessment as to whether the crime scene DNA could have come from that person.
Can be compared to the national data bank to see if you can make an assertion as to whether the DNA could have come from a specific person
Sources of DNA
blood semen saliva skin cells hair roots foetal material finger/toenails body tissue e.g. from musclar tissue bone teeth
most common sources of DNA at crime scenes
blood
semen
saliva
sources of DNA - skin cells
Usually requires a more sensitive DNA profiling technique because there is very little DNA that is recovered from skin
sources of DNA - hair roots
Hair in your hairbrush or shed hair usually doesn’t contain DNA in the root of the hair, so can be hit or miss
Hair can be useful if it has been pulled out of the head and therefore still has the hair root attached
sources of DNA - foetal material
In criminal paternity cases, the foetal material can be DNA profiled
Sources of DNA - teeth
The last four are what you are typically dealing with in a body identification/DVI context especially if the bodies are not fresh, have been burnt or have been underwater for some time
Bone and teeth more difficult to process and to extract DNA
Fingers/toenails and deep body tissue from muscular material are usually straightforward to handle
Types of DNA samples list
Case samples
Reference samples (case specific)
From suspects
From other people involved
Types of DNA samples - Case samples
Samples taken from a crime scene
e.g. assault at the house then samples can be taken from the house, victim/deceased person is a crime scene in themselves
DNA profiles are not very useful unless you have something to compare it to therefore you have reference samples
Types of DNA samples - reference samples (case specific)
From complainants (the person who makes the complaint in a legal proceeding) In sexual assault cases, you get a reference sample from the complainant because any DNA that you recover from her you need to know what is her DNA (which you can compare to the reference sample which is usually a cheekswab) or if there is DNA present that is foreign to her and by having her reference sample if you get a mixture of DNA from victim and other people then you can determine the DNA profile of someone else
Types of DNA samples - from suspects
Samples from person’s of interest
Types of DNA samples - from other people involved
e.g. ambulance staff treated victim then it can be useful to get their samples as references, or if other people live at the house getting their DNA samples for reference so that you can see whose DNA is there legitimately
DNA profile databank is legislated under …
Criminal Investigations (Bodily Samples) Act 1995
DNA profile databank holds DNA from …
From convicted criminals (permanently held)
From volunteers (can be removed on request)
From people Police intend to charge (temporarily held (until conviction (then would be permanently held) or if the charges are dropped (where their profile is removed))
So in the normal course of investigation, we can compare our profiles from crime scenes or victims to reference samples from known people or to the databank as a whole
NZ does not have a missing person’s databank
DNA databank profile matching process
When you have an unidentified profile from a crime scene (when you know it is not the victim but you think it might be the offender), it gets loaded onto the crime sample databank and then this gets compared to all of the other profiles in the crime sample databank because it is sometimes interesting for the police to see if there is a pattern of offending (if that profile turns up in a whole lot of other crimes)
All crime profiles also get compared to the DNA profile databank in order to be able to provide the police with a person of interest that they can then go and investigate
YSTR crime sample databank - specific DNA sampling for the male chromosome which is the Y chromosome (other DNA profiles are generally looking at the DNA that is in all of our cells), databank that specifically catches Y chromosome profiles from case samples that are thought to be linked to the offender
DNA profile databank =
Profiles from people
n>214000
Crime sample databank= =
profiles from crimes
n>48000
YSTR crime sample databank =
YSTR haplotypes from n>550 crimes
What is stirred in the YSTR crime sample databank …
YSTR crime sample databank - specific DNA sampling for the male chromosome which is the Y chromosome (other DNA profiles are generally looking at the DNA that is in all of our cells), databank that specifically catches Y chromosome profiles from case samples that are thought to be linked to the offender
DNA laboratory process - summary
sample - extract - quantitate - amplify - profile
DNA laboratory process - 1) sample
Sample - Take a small enough sample to fit into a small tube or beaker
e.g. swab (mouth, blood), small piece of fabric
DNA laboratory process - 2) extract
Extract - Extract cellular material from substrate and then isolate DNA from cell
Get material off fabric, surface etc
DNA laboratory process - 3) quantitate
Quantitate - Estimate how much total human and male DNA is present
Estimating how much is useful for the amplifying step
Most offenders are male
Sexual assault DNA profile from a sexual assault kit done by a female complainant, you do the DNA profiling process and you get to the stage where you estimate how much human and how much male DNA is present and if there is no male DNA present then some countries stop processing this case but in NZ laboratory they have YSTR profiling which just looks at DNA on the Y chromosome so even if there is not enough cellular material from the male for their quantitative system to detect then the Y chromosome specific one may be able to detect it
DNA laboratory process - 4) amplify
Amplify - Amplify DNA by making many copies of the areas of interest (PCR)
DNA laboratory process - 5) profile
Profile - Separate and detect the profiling results (electrophoresis)
Detect the amplified DNA using electrophoresis which gives a DNA profile that can be analysed
DNA laboratory process - 5) profile
Profile - Separate and detect the profiling results (electrophoresis)
Detect the amplified DNA using electrophoresis which gives a DNA profile that can be analysed
DNA in an individual comes from …
half comes from mother and half comes from father
in NZ …
In NZ, have different kits that look at different sites on the DNA molecule, one that looks at 15 different sites and another one that depicts 21 different sites
Green bars at the top on an DNA profile
Green bars at top relate to a locus which relates to the general area that this result comes from
Peak on a DNA profile
The peak relates to how long the fragment of DNA is
can tell a DNA profile is from a female vs a male because?
Can tell these profile is from a female because at the locus Amel there is only a single X peak and if this was a male then there would be an X peak and then a Y peak just adjacent to it
Crime scene vs normal DNA profile
Can tell this sample is not from a crime scene, crime scene is often degraded and often don’t have enough to work with whereas this one is well balanced from left to right
DNA from more than one person because at the loci there are more than one peak and the peaks are not particularly well balanced, some DNA that has come from one person in a greater proportion and then there is DNA from another person in a different proportion
DNA profile
Set of profiling results obtained
locus
A specific area or site on the DNA (plural: loci)
allele
An individual DNA profiling result
DNA and body identification
DNA isn’t always the best technique in a body identification or DVI scenario
DNA extraction and state of body
Fresh –> Easy, just take blood from chest cavity
Decomposed
Skeletal
Burnt
Complete or incomplete (fragmented)
Last four makes DNA analysis quite difficult and problematic
Operation Earthquake Identifications
Christchurch earthquakes identification
DNA didn’t really feature during the operation earthquake
Primarily fingerprints and odontology used for identification
There are some scenarios where DNA profiling is the only course of action or if there is something uncertain about the original identification then the DNA profile can provide a backup
Why DNA is not always the best technique
DNA profiling requires a specialist laboratory and is slower (although “Rapid DNA” technologies will change this)
In NZ this is based in Auckland, therefore there is a bit of a time delay as samples need to be transported to this location
Samples have to be transported to the lab
Blood and tissue samples take ~2 days from receipt to report
Bones and teeth take longer
They have to be cleaned and ground to powder (need to be crushed)
We also need to process reference DNA samples
Putative reference samples: Toothbrushes, clothing, other personal items, Guthrie cards
Can take time for the police to gather these
Toothbrushes can be a problem, usually find more than one person’s DNA due to the close proximity of one toothbrush to others
Or samples from direct family members (which can be a problem if entire families are involved in the disaster.)
Such as parents or children of victims who are believed to be involved in the disaster
sometimes DNA is the only option
When there is no real clue of who the person is, then DNA is a good bet, could match to something on databank or could even match to family members that are on the databank
When there are no teeth or dental records
When there are no hands/feet or comparison records
In Christchurch earthquake, police looked for these records in people’s houses who were believed to be deceased to find fingerprints and footprints to try match people to their identity
The DNA Profile Databank and familial searching can help if the body is really unknown
Familial search - if you have a crime sample or a profile of someone who can not be identified then can do a direct comparison to all of the DNA profiles held on to the data bank to see if there is a direct match or you can also do a familial search which can identify directsiblings, parents and children of the unidentified individual (can be useful when there is no clue to who the person actually is)
Sometimes the Coroner really wants to be sure about the identification
DNA provides a back up to fingerprints etc (other forms of identification)
Operation Whakaari
(White Island) (22 people were killed) (disasters come in all shapes and sizes)
Volcano added complexity that hadn’t had to be dealt with previously in DVI case work in NZ
Entire family groups were on island.
Putative references were from cruise ship cabins (but we didn’t know what belonged to who)
Difficult initially because the only reference samples were from the people’s cabins, hard to identify who used a certain toothbrush of the people in the cabin, added a level of complexity as to trying to determine who the deceased were when comparing them to these references
One cabin that was a mother and daughter, could tell mother and daughter from DNA profiling, from DNA couldn’t say who was who and the condition of the bodies also created difficulties, Australian Federal Police got samples from mother’s parents and then figured out a family tree which led them to figure out who was who
Additional support from Australian Federal Police
The sulphur and other chemicals/acids/heat added to complexity
Affected the bodies
From the pathologist knew that the corrosive nature of the chemicals that were in the air and also the superheated air damaged the bodies
Oral cavities quite badly damaged because of the superheated air, so instead took blood from the chest cavity
Blood and bladder swabs from the body so not that concerned about contamination
We had concerns about corrosive affects on our instruments
Took items from the island such as shoes, scared that ash etc it would affect the equipment, consulted chemists
other considerations with DNA sampling - body parts
DNA profiling may not be needed
Important to repatriate body parts with the rest of the body
Sometimes there are instances where this is not required, sometimes pathologists can determine body parts
Return body as intact as possible to the family, if the body part is very small that through DNA profiling it may consume majority/the entire body part/tissue then they may decide not to process that part
other considerations with DNA sampling - cross contamination
Multiple bodies in one event
Mortuaries are not forensic DNA labs
In forensic DNA labs it is very important that there is no cross contamination, you have to be certain that the DNA profile we have obtained is from whatever sample you are dealing with, mortuaries are less concerned about this because their main goal is to find the cause of death and identification of the body
other considerations with DNA sampling - sample from protected areas
Usually samples from within the body i.e. internal samples
Internal samples if body intact
Blood from chest cavity is better than a mouth swab
If the body is reasonably fresh
Could also be deep tissue or bladder swabs
Boots protect feet (toenail samples are great.)
Sample types - fresh bodies
Fresh bodies
Blood from chest cavity
Sample types - decomposed
Finger/toenails
Deep muscle tissue (i.e. psoas)
Bones/teeth (last resort)
These can be a bit more problematic for the DNA extraction
Teeth are not taken out until checked by odontology and examined by them
sample types - skeletal (dependent on environment)
*Long (weight-bearing) bones (in the legs)
These are the best bones to take DNA profiles from
If the bone still contains marrow, this is usually useful
A bit of burning is ok, but too much means there is no way you can get a DNA profile (bottom two images)
Teeth
sample types - burnt bodies
Bladder swabs
Bladder is quite well protected within the torso, urine is quite sterile and the bladder is a wet environment, works well for severely burned bodies that cannot be identified in other ways
Deep muscle tissue (i.e. psoas muscle)
Fingernail/toenail may be successful
Bones/teeth
Last resort
