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DNA Laboratory

The DNA Laboratory comprises three separate units, the Nuclear DNA Unit, the Mitochondrial DNA Unit and the CODIS (Combined DNA Index System) Unit which includes a CODIS Administrative Section and a CODIS Laboratory Section. Each is tasked with assisting law enforcement agencies throughout the State of New Jersey in solving crimes utilizing state of the art DNA technology.

For evidence submittal to the Forensic Serology Unit, see the Evidence Field Manual link on the OFS home page.


The Nuclear DNA Unit

The Nuclear DNA Unit receives physical evidence containing biological stains (blood, semen, or saliva) from crimes involving homicides, sexual assaults, kidnappings, aggravated assaults, and burglaries. The laboratory currently targets 15 specific regions found along the chromosomes known as short tandem repeats (STR). The stains are subsequently analyzed for DNA using a four-step process: extraction, quantitation, amplification and detection. The subsequent STR genetic profile that is produced from analyzing a piece of biological evidence can be directly compared to the genetic profile of a reference control sample from either a victim or suspect. From this comparison, a scientist can conclude whether a person is included or excluded as the source of the stain. Profiles from evidentiary items can also be uploaded to the CODIS database and searched against other unknown forensic profiles, convicted offender profiles and arrestee profiles Ė a powerful tool when a crime occurs and there are no leads to a possible suspect. When a forensic unknown profile matches the profile of a reference sample, a scientist performs a statistical evaluation to give weight to this match. Typically the chance of selecting a randomly chosen individual that matches a full genetic profile is less than 1 in a quadrillion. A quadrillion is 1 followed by 15 zeroes. In addition to writing reports, DNA scientists are often called to court to testify as to the results and conclusions of their analyses.

The Nuclear DNA Unit also has the capability to analyze biological evidence for Y-STR's. Y-STR analysis is specific to the Y chromosome, and targets only male DNA, invaluable when a mixture of female and male DNA is present (e.g., sexual assault cases). While this can be a very useful tool, the Y-STR profile and resulting statistics are not as discriminatory as those typically found in an autosomal match. This is due to the fact that all paternally related male individuals share the same Y-STR profile. An individual who does not match the Y-STR profile can be positively excluded as the source of the Y-STR profile. However, when a person matches the Y-STR profile he is included with a host of individuals that may have this same profile. Because Y-STRís are passed on from father to son, all male paternal descendants are expected to share the same Y-STR profile. This characteristic is advantageous because sometimes the proper reference samples needed for nuclear DNA comparison are not available (e.g., missing persons or mass disasters). In these situations, any direct male paternal descendant may be used for comparison purposes.

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The Mitochondrial DNA Unit

The Mitochondrial DNA Unit began analyzing biological samples for mitochondrial DNA (mtDNA) in the fall of 2005.  Typically, mtDNA analysis is utilized for those specimens where the quality and/or quantity of DNA are insufficient for nuclear DNA analysis. Mitochondrial DNA analysis is also utilized in missing persons/unidentified remains cases where maternal relatives are the only available reference source.

Advantages of mtDNA

Sturdiness:
Because of its structure, location, and high copy # within the cell, mtDNA is much more robust than nuclear DNA and is more likely to be found in old, degraded and environmentally damaged samples. Mitochondrial DNA is also more likely to be found in samples that contain very little nuclear DNA to begin with, such as hair shafts, bones and teeth.

Maternal Inheritance:
Because mtDNA is passed on from mother to child, all maternal relatives are expected to share the same mtDNA profile. This characteristic is advantageous because sometimes the proper reference samples needed for nuclear DNA comparison are not available (e.g., missing persons or mass disasters). In these situations, any maternal relative may be used for comparison purposes.

Suitability of mtDNA Analysis

Because nuclear DNA analysis is more discriminating than mtDNA analysis and has the potential for identifying the source of the DNA, nuclear DNA analysis is usually the preferred method of testing. However, when items of evidence contain little or no nuclear DNA, or proper reference samples aren’t available to compare to the evidence, mtDNA analysis becomes a powerful investigative tool. The results can provide an important link between victim, suspect, and /or crime scene and can also conclusively exclude an individual as being the source of a mtDNA profile.

The majority of cases in which mtDNA analysis is performed involve hair evidence where only the hair shaft is present. Mitochondrial DNA analysis is also justified for hair evidence where no tissue is present on the root. A hair examination needs to be performed prior to mtDNA analysis to determine that the hair is human, its suitability for comparison to known reference hairs, and its suitability for nuclear DNA analysis.

Mitochondrial DNA analysis in unidentified remains cases is appropriate only when a forensic anthropologist and/or forensic odontologist can verify bone or teeth specimens as of human origin. During the examination, the best specimens for DNA analysis will be selected.

Current available techniques cannot effectively distinguish between sources or relative quantities of mtDNA. Consequently, mtDNA is not appropriate for evidence containing possible mixed sources of DNA such as semen stains from sexual assaults, fingernail scrapings, clothing, and “touch DNA” such as doorknobs, steering wheels, telephone receivers, etc.

In addition to criminal casework, this laboratory will process samples from missing person’s cases and subsequently upload the results into a missing person’s index within the CODIS database. This will assist law enforcement agencies in bringing closure to families missing loved ones.

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