The Mitochondrial Section

In 2003, the FBI appropriated 4 million dollars in funding for a partnership to operate mitochondrial units in 4 regions of the United States.  Connecticut was chosen to be one of those four labs, along with labs in Arizona, New Jersey and Minnesota.   The funds provide for personnel, training, equipment and supplies required to perform mitochondrial trace and DNA analysis.  This will assist law enforcement in identifying missing persons and in resolving criminal cases.  This partnership greatly extends the testing abilities of the CT State Forensic Laboratory.  The caseload is expected to be approximately 120 cases annually; each case is expected to take 6-8 weeks from start to completion. 

The Mitochondrial Section of the CT State Laboratory is made up of the Mitochondrial DNA Unit and the Mitochondrial Trace Unit.  Each section contributes a necessary role so that the mitochondrial evidence obtained is utilized to its fullest extent possible. 

Throughout the commission of a crime, there is a possibility that a transfer of hair can occur between individuals and/or objects.  A search of the crime scene and individuals involved can result in the collection of these hairs.  The number of hairs on the average person’s head, the rate of an individual losing an average of 100 hairs per day, and the numerous physical characteristics exhibited in human head and pubic hairs all demonstrate the need for forensic hair comparisons.  By examining and comparing the macroscopic and microscopic characteristics of the hair, an examiner can determine many things.  First and foremost, the determination can be made as to whether the evidentiary item in question is indeed a hair.  If it is, several other questions can be answered: if the hair is human or animal, if it is human, from which part of the body it originated, the racial origin of the hair, whether the hair was forcibly removed or naturally shed, and lastly if the hair is cosmetically treated, damaged, or diseased.  The final judgment then can be made regarding whether a known hair sample can or cannot be excluded as the source of the hair in question.  A hair that is associated with a known sample can then be sent to the Mitochondrial DNA Section for further analysis if it has been deemed unsuitable for nuclear DNA testing, (i.e. there is no tissue present). 

It is a common misconception that the only DNA found in the cell is contained in the nucleus.  While this is the only DNA that is unique to an individual, mitochondria, organelles in the cell’s cytoplasm, contain their own genome that has been passed to the child solely from the mother.  While this does not allow for the mitochondrial DNA (mtDNA) sequence to be unique to an individual, its high copy number in cells allows for it to be available in those cases in which nuclear DNA is absent.  Samples where nuclear DNA is unsuitable could include hairs in which no root is present (as previously discussed) bones, and teeth.  The Mitochondrial DNA Section will receive samples deemed suitable for mtDNA testing from other sections of the laboratory and law enforcement agencies.  The samples will then be processed to extract the DNA from the sample, amplify that DNA, and eventually sequence it to obtain the mtDNA type for the regions desired.  These sequences will then be compared to known sequences obtained, as well as searched against a database to determine its frequency in the general population. 

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The Mitochondrial Section of the laboratory includes two Lead Criminalists and seven Criminalists who, combined, have over 45 years of forensic experience.  The Lead Criminalist of the Mitochondrial Trace Unit has a Master’s degree and has experience in forensic hair examination and other forensic disciplines.  She coordinates with one Criminalist and together, they collect, preserve, examine and compare hair evidence, write reports and testify to their findings in a court of law.  The Lead Criminalist of the Mitochondrial DNA Unit has a Doctorate and experience in the principles of DNA analysis, allowing him to be a strong technical leader for the section and liaison between the CT State Laboratory and the FBI.  He coordinates six Criminalists: Four biologists who perform all the necessary lab work on case samples from DNA extraction to sequencing, and two examiners who analyze and interpret the DNA sequences, write reports, and testify to their findings in a court of law.  Together, all nine work as a team to get results in an expedient and accurate manner.

To continue the look into mitochondrial DNA testing and hair analysis, please click here for a PowerPoint presentation.  In it, you will find a more involved description of the type of testing done on the samples, a brief description of the analysis, as well as some interesting cases that have used mitochondrial DNA testing. 

Mitochondrial DNA.pdf

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