For our laboratory
colleagues
For details about sending us a case, please
look under Submit
a Case.
We are often asked about the "best"
samples for testing. Generally, for hair submission:
- We suggest that you select candidate questioned
(evidentiary) hairs based on their probative
value. For example, a hair taken from the
floor of a public restroom near a victim's
body may be
less informative than a hair found on the
victim. Samples can be prioritized to save
financial resources. We can perform your testing
accordingly.
- We suggest that a qualified hair examiner
evaluate evidentiary hairs with respect to
each other. Microscopic hair comparison may
be less valuable as a tool to compare questioned
hairs to the exemplar hairs of known individuals
than as a tool to compare questioned hairs
to each other. Then, depending on their probative
value, candidate hairs can be selected from
groupings of
similar hairs for testing.
- All other variables being equal, such as
equally probative and similar-appearing hairs,
we prefer
to take a portion of a longer hair, rather
than consume an entire hair. Preservation
of evidence is important whenever possible.
In general, the size of hair sample taken
for testing will be approximately 2cm, if
available, but this varies according to numerous
considerations. We do not advocate against
testing small hairs simply because of their
size and because they will be consumed. We
have successfully analyzed hairs as small
as 2 mm and the challenges of testing small
hairs are similar to the challenges of testing
any small or old sample. In the event that
a hair is consumed, a review of the laboratory
case folder by opposing counsel (discovery)
is more desirable than not testing
potentially informative evidence.
- Reference samples provided for comparison
to hair samples do not need to be hairs.
In a rare case, hairs might be requested for
a reason. However, in most cases, a buccal
swab, saliva, or blood reference known is
acceptable. We will discuss with you any situation
in which a family reference sample might be
needed when a direct reference sample from
an individual is unavailable.
- Hair samples may be submitted on slides,
post-it notes, tapelifts, in small tubes,
paperfolds, coin envelopes, or zipper seal
plastic bags. If hairs are mounted on slides,
we prefer to remove the hairs from the slides
ourselves, as reduced handling reduces the
possibility of contamination. However, the
exception to this rule is if hairs and trace
(fibers) are all mounted together on slides,
we prefer that either the trace be removed
or that the hairs be removed and repackaged.
- In any case, we recommend that any necessary
microscopy or photodocumentation of hair or
other evidence be completed prior to sample
submission.
Here are some general thoughts on skeletal
sample submission:
- Unless very old, skeletal remains are usually
very successful samples. In order of preference,
we
prefer these bones due to the likelihood of
their containing good quality mtDNA: tooth,
long bone
(femur, radius, humerus, ulna, tibia, fibula),
rib. However, any skeletal
material can be tested,
even the smallest fetal remains.
- For teeth, in order we prefer: unreconstructed
molar/premolar, unreconstructed canine, unreconstructed
incisor, teeth with dental work. We remove
the dental work and return it.
- Approximately 0.4 g of powdered tooth or
bone is used in an analysis. Remaining bone
powder is
returned along with uncut skeletal or tooth
samples.
- Again, we recommend that any necessary microscopy
or photodocumentation of skeletal evidence
be completed prior to sample submission.
Other samples:
- We have tested many sample types, including
fingernails, organ tissue (slides, paraffin),
cigarette butts, touched or licked objects,
fabric cuttings, surface swabs, and clothing
swatches, among others. Please call us to
discuss the limitations of mitochondrial DNA
analysis on some of these sample types.
DNA extract:
- Occasionally we are asked about testing
the DNA extraction product from another laboratory
for
mitochondrial DNA. We are able to do this
if specific conditions are met. Please contact
us to
discuss your case.
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