STR
Although each person’s DNA is unique to the person (not counting twins), large portions are identical to the DNA in other people. In fact, the vast majority of a person’s DNA is the same as any other human’s. The DNA locations that do vary are called polymorphisms, and to create DNA profiles, STR DNA testing focuses on these areas, which are on autosomal chromosomes inherited from biological parents.
Short Tandem Repeat testing is one of the most common forms of DNA testing in use today. It searches out repeating patterns in the DNA building blocks (nucleotides) that make up polymorphisms and, essentially, maps them. The locations and spaces between them make up profiles that can then be compared to other STR profiles to, for example, see whether a suspect’s DNA matches the DNA left at a crime scene.
Y-STR
The Y chromosome is a short section of DNA that biological males carry. The same Y chromosome is passed from father to son and stays relatively unchanged through generations.
Y chromosome DNA typing (Y-STR) seeks out short tandem repeats (described in the section above) only on the Y chromosome. The resulting profile identifies a paternal line, not necessarily a single person. But combined with further detective work, it can provide a powerful lead in a criminal case.
Familial DNA Testing
Familial DNA testing is a search for DNA that is so similar to the target profile that it could come from a family member. Such tests, which require a special software that searches DNA samples in the CODIS database, require more resources and, therefore, are used only in certain cases, such as those that present an ongoing risk to Ohioans.
If potential matches are found, scientists take a look at one chromosome, the Y chromosome, which is inherited in male lineages. Every male’s Y chromosome exactly matches his father’s, paternal grandfather’s and those of any brothers and sons he has.
When a Y chromosome from crime scene evidence matches a known person’s Y chromosome from that CODIS search, Criminal Intelligence analysts go to work establishing the family tree of the known person. They research whether any of the person’s same-sex relatives could have committed the crime, including whether the relative would have been old enough (or young enough) and whether the relative was known to have been in the area when the crime occurred.
If such a person is located, further DNA testing is used to confirm that the crime scene DNA does, in fact, match that person's DNA.
MPS
Massively Parallel Sequencing (MPS) or Next Generation Sequencing (NGS) refers to a range of new technologies that have revolutionized genomic research over the past decade. MPS enables millions of fragments of DNA from a single sample to be sequenced in unison rather than one at a time.
For Ohio families, MPS can bring answers about missing loved ones and shed new light on cases previously considered unsolvable. Compared to traditional DNA testing methods, MPS is significantly faster and more sensitive, and it allows for more detailed information to be generated from DNA.
Mitochondrial DNA Testing for Project LINK
Massively Parallel Sequencing (MPS) makes possible the testing of mitochondrial DNA (mtDNA), a process that BCI has implemented in partnership with Battelle Memorial Institute. BCI, one of the first state crime labs to implement MPS-based mtDNA testing, uses the tool exclusively for Project LINK casework in missing persons cases.
mtDNA offers numerous benefits in cases that otherwise have gone cold or in which all other types of DNA testing have been exhausted.
Traditional DNA testing performed at BCI requires nuclear DNA to be present. Nuclear DNA is a fragile molecule with only two copies per human cell. In cases where samples are old or have been potentially damaged by environmental factors, nuclear DNA might have broken down, making successful testing impossible. Unlike nuclear DNA, mtDNA is a robust molecule with 100 to 10,000 copies per human cell. In cases in which nuclear DNA is extremely degraded, there is a very good chance that larger numbers of intact mtDNA are available for testing. The MPS-based mtDNA testing at BCI takes advantage of this robust and plentiful molecule to generate new information for old cases.
In contrast to the previously described Familial DNA testing, which is based on paternal (male) lineages, mtDNA is maternally inherited. This means that each individual in a particular maternal lineage has the same mtDNA profile. Therefore, if an mtDNA profile from a missing person or from unidentified human remains is obtained, any individual from the mother’s side of the family could be used to make a connection between that family and the remains. Even distant maternal family references can be used in cases in which direct references are unavailable.
It is important to remember that mtDNA testing is maternal lineage-based. Similar to the paternal lineage-based Familial DNA testing, any mtDNA-based match is not a unique identifier and must be considered alongside other forensic and investigative information.