Forensic mtDNA and Disaster Victim Identification Flashcards
LO
*** Explore the challenges associated with DVI
* Understand phylogenetics and how we can apply this to improve quality standards
* Evaluate when to use mtDNA in casework, and what the advantages and disadvantages of such decisions are **
What are the uses of mtDNA in forensics?
- Criminal casework/ identification
- Relationship cases
When was mtDNA first used in a forensic context?
The FBI laboratory began researching mtDNA in 1992 with a view to using it for human identification and the first casework was analysed in June 1996
Why is mtDNA useful over nuclear DNA in forensics?
- The high copy number, circular shape and cellular location mean mitochondrial DNA is often present in cases where nuclear DNA is not- in cases of DNA or generally we are much more likely to find mitochondria
- This particularly applies to very old or severely degraded DNA. For example, ancient bones or fire victims
- It is also useful for tissues poor in DNA, for example hair shafts
Why is mtDNA useful for hair samples?
- Hair samples are problematic- even world leading labs only have an 85% success rate
- Success is lower in coloured (dyed) hair
- The amount of recoverable mitochondrial DNA decreases with increasing distance from the hair root
Casestudy
Clothing and personal effects…
* A ‘book of belongings’, a joint effect between the ICMP and ICRC, is shown regularly to relatives of the missing, and may provide a ‘presumptive identification’
o Contained 800 different items
o Only 281 were identified as to belonging to someone who was missing
o Did DNA testing for the 54 potential identifications, and >20 was incorrect
o 30/281 were correct identification
o From this point on, DNA became more DNA focussed
2004 Indonesia earthquake
- The bodies in water made it hard to recover DNA
- In these situations, dental records are more useful than DNA
With post-mortem sample collection, what samples should be collected and how much where applicable?
- Soft tissue- deep red muscle (1g)
- Bones- recommended a window section from a long bone
- Once ground up, can use <1g of bone material in extraction with newer extraction methods
- Femur & Teeth (healthy molars) preferable
For Ante-mortem sample collection, what should be collected?
Give information regarding why and also pros and cons of this sample collection method
- For missing people, recommended collection of 3 related family samples (kinship testing)
o Want at least 3 people because, some people may not know their family or may think they do but 2% don’t, so want multiple references. And some samples are better than others - Some relatives are more useful than others, in general the more reference samples are better
* Direct samples can be collected (want multiple samples to ensure you have the right DNA)
o Razor, toothbrush, comb etc
o Medical, military, birth samples
*** Advantages **
o Statistical match is very simple, should be an identical match
*** Disadvantages **
o Can you be sure that these samples are correct?
Direct reference classification for anti-mortem sample collection
World Trade Centre 9/11
- Degraded DNA a very important factor due to the circumstances
- Extreme heat (>1000˚c with fires burning for >3 months)
- Extreme physical trauma (pressure of building collapse)
- Environmental degradation- recovery of 20,120 biological specimens between September 2001 and May 2002
o By water, UV light etc - Receiving skeletal samples at the rate of 400-800 pw (>12,500 in total)
- Over 5,500 DNA extracts from soft tissue
- Plus, refence samples
- In total 7916 human remains were identified using DNA techniques
- Of the 2749 victims, DNA was a contributing factor in the identification of 465 people and the sole evidential took in the further identification of 817
- Other main methods included dental records and fingerprints
- Identification efforts ceased in February 2005 with 1588 (58%) of victims identified
- Most recent ID August 2017- 1641/2753 victims ID’s
- DNA identification of these severely compromised samples was possibly due to the techniques discussed
- All samples were first analysed for standard STR typing and 52,528 STR profiles were generated
- For samples failing to produce adequate STR profiles, further analysis was performed
- Mitochondrial analysis generated 31,155 sequences (later revised to over 44,000)
- SNP typing produced 16,938 SNP profiles
How is mtDNA inherited?
What can it therefore be used for?
As mtDNA in inherited maternally, it can be used to help clarify relationships
Tell me about the first historical DNA Forensic investigation
- The first historical DNA forensic investigation was performed in 1944 using mtDNA
- The Russian Royal family was executed in 1918
- Bones believed to belong to Tsar Nicholas II, the Tsarina and their children were analysed for mtDNA
- The results were compared to living maternal relatives, including Prince Philip, and a match was made
- The Duchess Anastasia was absent from the grave
Phylogenetic tree
‘Mitochondrial eve’ is where the common ancestor descends back to
- The blue line represents migrations that have occurred from that
- The other coloured lines are also mutations
- Some people have Ancestral ‘A’, some people have one base chance from the ancestral which is denoted by ‘B’ and ‘C’
Mitochondrial testing example
- This is an HVI sequence from an individual living in London whose recent ancestors were born in the Caribbean. Shown are the bases that differ from the rCRS (revised Cambridge Reference Sequence)
- T16126C, A16165T, C16187T, T16189C, C16223T, C16264T, C16270T, C16278T, A16293G, T16311C
- This means for instance that for C16223T, there is a change of C–>T at position 16223
o C16223T= L Haplogroup (African)
o C16278T= L1 or L2 Haplogroup
o C16187T, T16189C, T16311C= L1 haplogroup
o T16126C, C16264T, C16270T= L1b Haplogroup
o A16293G= L1b1 haplogroup (predominantly West Africa)
o A16165T= Private mutation
Therefore, due to the maternal inheritance of mtDNA, what can it also help to do?
- Maternal transmission of mtDNA without recombination
- Can trace back accumulation of changes of study population migration
- Back mutations are rare except at hypermutable nucleotides
- Hence can class specific profiles into haplogroups
- Can help trace people’s ethnic origin
Mitochondrial control region
The mitochondrial control region is known as the D-loop and sits between 16024 and 526 bp
And contains 2 hypervariable regions
A hypervariable region (HVR) is a location within nuclear DNA or the D-loop of mitochondrial DNA in which base pairs of nucleotides repeat (in the case of nuclear DNA) or have substitutions (in the case of mitochondrial DNA). Changes or repeats in the hypervariable region are highly polymorphic.
Reference control region sequencing
Midi-mito control region sequencing
Mini-mito control region sequencing
Whats the procedure for Capture mitochondrial DNA analysis ?
Full genome matches
