Contamination Flashcards
Define contamination?
- to make something impure by exposure of or an addition of a polluting substance
How does the new DNA17 multiplex make contamination easier?
- it is very sensitive so capable of detecting even smaller amounts of DNA
- improved sensitivity = contaminated DNA is more likely to be detected
What is difference between contamination and adventitious transfer?
- contamination - applied to forensic process as transfer of foreign DNA to sample AFTER crime has been discovered (scene attendance through to sample collection/testing)
- adventitious transfer - transfer from innocent activity before crime event
What is the issue with undetected contamination?
- complicates interpretation
- increases risk that result could is incorrectly attributed
- increases risk that result is given undue significance
- could diminish the value and reliability of the forensic evidence
- could change single source sample into a mixture
- could give a false positive result
What are the two constituents that contamination could manifest as?
- major and minor
What are the two types of contamination that it could be?
- one off - affecting single tube in batch of samples
- blanket/gross event - affecting whole batch of samples
What are the 3 criteria that need to be fulfilled for contamination?
- needs to be:
- source of DNA available to be involved in transfer event
- opportunity for DNA transfer to occur
- mechanism by which DNA transfer is achieved
What are the first potential sources of contamination?
- individuals involved in different roles of forensic process:
- police
- scenes of crime officers
- pathologists
- forensic scientists
What are the second potential source of contamination?
How can this be understood and therefore avoided?
- consumables or reagents used in forensic process, packaging and environment in which test is carried out (including other forensic samples processed in lab environment)
- important to understand where our consumables are produced and the quality standards which are associated with their manufacture
- essential to have quality managed lab process with appropriately trained staff
What are three contamination opportunities?
1 - from person to stain
2 - from consumable to stain
3 - from stain to stain
What can be said about the mechanisms of transfer?
What are the three mechanisms for transfer?
- the mechanisms for transfer are provided by the opportunities and can be straightforward or more complicated
1 - direct primary contact
2 - secondary transfer
3 - tertiary
What is an example of person to stain contamination?
- poor use of PPE (facemasks and hairnet) which should provide a barrier between operator and sample
What is an example of reagent to stain contamination?
- direct transfer from DNA already present in a tube which is not sufficiently free of DNA for forensic purposes
What can issues with lab processes cause?
- DNA transfer and contamination is facilitated inappropriately by cross-contamination between samples
How could we prevent contamination transfer?
- training of staff to a recognised standard (knowledge of what could happen and where to look for it)
of - procurement of consumables from a source supported by quality standards
