Through DNA testing, law enforcement officers are able to identify human remains or the individual responsible for a crime. DNA testing is a highly advanced scientific process that involves replicating the human DNA sequence to create a genetic map of an individual. Because of its reliability, DNA testing has become a significant factor in criminal cases. However, it has also been identified as having the potential to violate privacy and constitutional rights.
Process of DNA Identification – How Does it Work?
The DNA identification process consists of five stages: isolation, quantification, polymerase chain reaction (PCR), short tandem polymerase chain reaction (STR-PCR) and interpretation. Isolation refers to the extraction of DNA from the nucleus of tissue cells. After extraction, scientists quantify the DNA sample by ensuring that it is at least one billionth of a gram in size. If the sample is smaller the isolation process must be repeated. Next, through PCR, the single strand of DNA is split down the middle into two pieces and replicated to create a larger sample. Subsequently, through STR-PCR, smaller sections of the DNA sequence are replicated, permitting scientists to interpret the DNA and create a genetic profile of the individual from whom the original DNA sample derived. On average, a DNA test can take between five and ten days to complete.
How Effective is DNA Identification?
DNA testing is not 100% reliable, but is pretty close. In DNA, a match of nine of the thirteen markers is considered sufficient to identify an individual. The Federal Bureau of Investigation (FBI) estimates that unrelated persons sharing nine markers is approximately 1 in 113 billion, indicating how reliable DNA testing can be. The imperfection of DNA testing derives from the fact that only a small portion of DNA is tested. While matching may be possible based on a small sample, a small sample is not always representative of an individual’s entire genetic makeup. Because of this, DNA testing is often allotted a small percentage of error, often a tenth of a percent. However, this does not prevent the results of DNA testing from being considered reliable in a courtroom.
- Accuracy of DNA “Matches” to Definitively Identify Suspects Questioned
- FBI Resists Scrutiny of ‘Matches’
- National Academic Press: The Evaluation of Forensic DNA Evidence
- The Innocence Project
About DNA Technologies Forensic Investigators Use
Forensic investigators use several different types of DNA technology. In Restriction Fragment Length Polymorphism (RFLP) a DNA sequence is split and replicated. The RLFP process requires a large sample size and is time consuming, resulting in it not being the preferred testing method. The more common methods of DNA analysis are PCR and STR-PCR Analysis, both of which were discussed previously. PCR is preferred because it permits DNA reproduction of older or smaller samples. STR-PCR Analysis is preferred because permits investigators to compare all 13 DNA sequences, making it possible to compare two similar-appearing samples. Investigators also utilize Mitochondrial DNA Analysis (mtDNA), in which DNA is extracted from the mitochiodrial cells and not a cell’s nucleus. Mitochondrial cells are transferred from mother to child, making it possible to determine ancestry and maternity. To connect a child and father, investigators perform the Y-Chromosome Analysis, in which the Y-Chromosome alone is analyzed.
Other Uses for DNA Forensic Identification
DNA forensic analysis is not limited to helping solve crimes. DNA analysis can be used to identifying victims of a mass tragedy, such as the September 11th Attacks or the Holocaust. Analysis has been used to solve historical questions about specific persons, such as whether any members of the Russian Romanov Dynasty survived the Bolshevik revolution. The travels of early humans and the heritage of wine grapes have also been traced through DNA testing. Recently, DNA testing has been employed to create a genetic database of endangered animal species. Using this information, scientists have even cloned animals. DNA sequencing has also been used to identify authentic sports memorabilia.
- The DNA Shoah Project
- Training and Assistance on Using DNA To Identify Missing Persons
- What can we learn from Neanderthal DNA?
- Other Uses for DNA Analysis
About CODIS: The National DNA Database
The results from STR-PCR analysis are entered into a federally managed database called “CODIS”. CODIS is short for the “Combined DNA Index System”. Currently, CODIS is comprised of two databases: the Forensic Index and Convicted Offender List. The former contains profiles developed from collected crime scene evidence, while the latter contains genetic profiles of convicted criminals. After receiving STR-PCR results, local and national law enforcement officers can check CODIS to see if any the database contains any matches. If there is a match between STR-PCR Analysis and CODIS, law enforcement officers may be able to identify the person or perpetrator of a crime. Operation of the CODIS system is regulated by the federal government.
- What is CODIS?
- CODIS and the National DNA Index System
- Federal Legislation on Forensic DNA
- State DNA Laws
Ethical Issues Involving DNA Databanking
While providing a reasonably reliable means to solve crimes, DNA testing has been criticized for the threat it poses to privacy. The information contained in DNA is limitless: hair and eye color, genetic diseases as well as ancestry can all be found in a DNA map. DNA samples are rarely destroyed, meaning that the information derived from a sample is potentially accessible by anyone. Debate also exists about whether law enforcement officers can demand and collect a DNA sample without probable cause because of the potential violation of a citizen’s Fourth Amendment rights against unreasonable search and seizures. Argument about collecting DNA extends to previously convicted felons and those under investigation. There is also argument over whether DNA Analysis should be usable in court in light of the fact that DNA findings are often highly persuasive to a jury regardless of their not being 100% accurate.
- The Chicago Study on Preventable Crimes
- US DNA Legislation
- Why Pass DNA Laws?
- Using DNA to Solve Crimes