mtDNA v. nuclear DNA
Mitochondrial DNA is present in rootless shed hairs, hair fragments, skeletal remains, and other samples too minimal and/or degraded for STR testing.
Law Enforcement Resources
For details about sending us a case, please look under Submit a Case
We are often asked about the "best" samples for DNA 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 rest room 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 stage 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 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 will be about 2 cm, if available, but this varies according to numerous considerations. We do not advocate not 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 blood or saliva 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, in small tubes, paperfolds, coin envelopes, or ziploc 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, with rare exceptions. In order of preference, we prefer these samples due to their likelihood of 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.
- About 0.4 g of tooth or bone is powdered and 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.
- 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.