Because of the way DNA scientists employ statistics, DNA is frequently regarded as the most trustworthy type of forensic evidence. Experts provide statistics that show how closely two DNA samples match when they compare the DNA found at a crime scene to the DNA of a suspect.
These match statistics can subsequently be taken into consideration by the jury when determining guilt or innocence. These match data are trustworthy because they are supported by thorough academic analysis. That study, however, only relates to DNA profiles also known as DNA fingerprints that have been produced with modern technology.
The category of biological evidences is quite diverse. It is a physical piece of evidence that has been categorized according to its type. The word “biological” is derived from the word “biology,” which refers to living things. Evidence, on the other hand, is defined as information that is utilized in a court of law to support a claim that has been legally presented to a competent tribunal as evidence of that claim.
The mathematical basis for computing match statistics when employing Next Generation Sequencing, or NGS, which generates DNA profiles that can be more helpful in solving particular crimes, has now been established by researchers at the National Institute of Standards and Technology (NIST). Forensic Science International: Genetics published this study, which was financed equally by the FBI and NIST.
“If you’re working criminal cases, you need to be able to generate match statistics,” said Katherine Gettings, the NIST biologist who led the study. “The data we’ve published will make it possible for labs that use NGS to generate those statistics.”
Therefore, biological evidence can be defined as biological elements or substances like hair, tissue, bones, teeth, blood, semen, or other body fluids or items containing biological material that are utilized to support and give a means of proving statements or claims in court.
How to Create a DNA Profile
Genetic markers, or regions of DNA where the genetic code repeats itself like a word being typed repeatedly, are examined by forensic labs to create a DNA profile. The amount of repeats at each marker in those segments known as short tandem repeats, or STRs varies from person to person.
If you’re working criminal cases, you need to be able to generate match statistics. The data we’ve published will make it possible for labs that use NGS to generate those statistics.
Katherine Gettings
The analyst just counts the number of repeats at each marker rather than reading the genetic code contained within them. This results in a string of numbers that can be used to identify a person, much like a lengthy social security number.
When genetic sequencing was extremely expensive in the 1990s, STR-based profiling was created. Currently, NGS makes sequencing affordable for purposes such as biological research. In contrast to conventional STR profiles, NGS can be utilized to construct forensic DNA profiles that contain the actual genetic sequence inside the markers. That offers a lot more information.
Since STR-based profiles typically contain more than enough information to properly identify a suspect, further information might not be required. However, the analyst might only obtain a partial profile, which might not be sufficient to identify a suspect, if the evidence only contains a trace amount of DNA or if the DNA has already started to break down due to exposure to the elements.
In some situations, the additional information in an NGS-based profile might aid in the case’s resolution. Furthermore, it can be challenging to assess the evidence that involves a combination of DNA from various individuals. In those circumstances, the extra information in NGS-based profiles can be beneficial.
Calculating Match Statistics
Because scientists have determined how frequently various versions of the markers appear in the population, DNA analysts may calculate match numbers for STR-based profiles. The probabilities of discovering a specific DNA profile at random can be calculated using those frequencies, exactly like the probabilities of choosing all the winning numbers in a lottery.
Years ago, NIST calculated the frequency of those STR genes using a collection of DNA samples from 1,036 people. The original samples, which were anonymized and provided by individuals who gave their agreement for their DNA to be used for study, were taken out of the freezer and utilized by Gettings and her co-authors to calculate gene frequencies for NGS-based profiles.
By sequencing 27 markers the core group of 20 that make up the majority of DNA profiles in the U.S. plus seven additional markers the scientists created NGS-based profiles for them. The frequencies of the various genetic sequences discovered at each marker were then computed.
It could surprise some people that researchers can infer gene frequencies from such a limited sample set. The NIST team, however, measured frequencies for specific markers rather than for entire profiles. The number of markers evaluated was more than 55,000 instead of 1,036, since they sequenced 27 markers, each of which was present in two samples.
NIST has already released the information required to create match statistics for NGS-based profiles, but more obstacles need to be overcome before the new method is widely adopted in forensics.
For instance, laboratories will need to create methods for managing the larger amounts of data generated by NGS. For the new technology, they will also need to create operational procedures and quality assurance measures. Still, while much work remains, said Peter Vallone, the research chemist who leads NIST’s forensic genetics research, “We’re laying the foundation for the future.”
