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Article #257: Dna Paternity Testing: Submitting Non-standard Samples (part 2)

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Success Rates for DNA Extraction from street and exposed to the elements (e.g.
Non-Standard Samples rain).
In part 1 of the article, we looked at Low (20% - 30%) For samples such as teeth
some of the more common non-standard or bone, where extracting DNA is a
samples used to obtain DNA from an relatively difficult and time consuming
individual for DNA testing purposes. In process, these normally need to be
this article we look at DNA extraction handled by a highly specialised
success rates from the various types of laboratory. In such cases, the individual
samples and how these can vary from one should consult the laboratory first to
sample to another. check their level of expertise, if they
Non standard samples do not always will accept the sample and the cost.
guarantee that a DNA Profile will be The classification above is however only
obtained. Whilst for buccal swabs it is a guideline, since as we have seen it is
possible not to obtain DNA, such as in not just the type of sample that is
cases where the swabbing was not important but also other variables can
adequately performed or else the swabs have an influence such as :
grows mould due to damp storage 1. Poor storage conditions (e.g. damp
conditions, in general problems with this environment, extreme heat etc)
type of sample are normally less than 2%. 2. Poor sample handling (possible
Therefore depending on the nature of the contamination with other DNA or dirt by
sample, there is usually associated a touching the sample)
High, Medium or Low probability of 3. Not enough DNA present (e.g. heavily
success in extracting DNA from each type used toothbrush vs used once only)
of sample (in some cases a percentage It is also important to note that the
probability of success is provided). success rate will also depend heavily on
High (80%) : For samples such as fresh the ability of the laboratory performing
blood stains or hairs with root where, the test. Not all laboratories that can
for a qualified and experienced DNA perform DNA Paternity testing on normal
laboratory, extracting DNA is considered swabs are capable of obtaining DNA from a
relatively straightforward. In such wide variety of other media. The more
cases, as long as the sample is handled difficult the media (e.g. teeth and
properly both during collection and bone), the greater the specialisation and
delivery to the laboratory, one can experience required to increase the
expect a high probability of success in chance of a successful DNA extraction.
extracting DNA. Finally, it is also important to note
Medium (50%-60%) : For samples such as a that with non-standard samples there is
toothbrush or cigarette butts the success always a risk that the extraction will
rate is influenced by a number of not work. Therefore any person
variables including heavy use vs light considering submitting such a sample,
use and/or storage conditions etc. especially where it may be only a limited
Therefore a heavily smoked cigarette butt sample available (e.g. person is dead),
found in an ashtray at home is more should take this into consideration.
likely to result in a successful DNA Selection of an experienced laboratory
extraction than a lightly smoked (possibly of forensic specialization)
cigarette that has been thrown on the will help minimize this risk.






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