EHocking
Penultimate Amazing
Fair enough, on the face of it. The reason I was curious was as to whether the lab was appropriately trained to determine species identification - especially as the particular test outlined in the letter is pretty much specific to sex determination.Following the letter, Paulides writes:The name of the lab has been removed because NABS has had problems with others calling the lab, stating they are with NABS and asking for results on specimens. If anyone has specific concerns or issues with this or the other letter in the book, contact a NABS member at any conference and we will gladly show you the results.
The fact that THEY had never encountered it, while exciting to a BF proponent, is not a reliable data point to make any conclusions.
I found this, the test manufacturer's handbook on the test system, GenePrint ® PowerPlex™ 16 System (PDF).
In the troubleshooting section there are a number of things that could throw up this unexpected peak:
Googling, there are a number of papers (many of which were beyond my ken) that discuss errors with this process, including misidentification of sex, let alone species.(Problem) Extra peaks visible in one or all of the color channels.
- Contamination another template DNA or previously amplified DNA
- Artifacts of STR amplification
- Samples not completely denatured
- Background (Load less amplification product or decrease the injection time.)
- Capillary electro-phoresis (CE) related artifacts (“spikes”)
- CE-related artifacts (contaminants)
etc etc
This particular sentence in this paper's abstract ("Validation and implementation of the PowerPlex 16 BIO System STR multiplex for forensic casework", is intriguing (my bolding),
"The mixture study results were comparable to those reported for other multiplex systems, the environmental study demonstrated a loss of larger molecular weight loci when samples were incubated at elevated temperatures for a prolonged period of time, and the only notable cross species hybridization was observed with primate DNA samples."
Does this imply that the PowerPlex system is liable to misidentify primate species?
I realise that this may seem like hyper-sceptical "denial" of the hair/DNA evidence, but in light of a 15min Google I was able to come up with a number of more plausible explanations for the anomalous result before only concluding, "...at this time it cannot be ruled out that this could be DNA from an undocumented species."
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