By: Uncovered Staff
Since the 1980s, forensic investigators and members of the criminal justice system have been using DNA to provide critical information that can be used to prove a suspect’s guilt or innocence. In addition to aiding in the solving of hundreds of active investigations and cold cases, forensic DNA analysis has also been used successfully to exonerate people who were wrongfully convicted of crimes.
Origin of DNA Testing
DNA, short for deoxyribonucleic acid, carries the genetic information responsible for living organisms’ development, function, and reproduction. It was initially identified in the late 19th century by Swiss chemist Friedrich Miescher, and then in 1953, American biologist James Watson and English physicist Francis Crick discovered DNA’s unique double-helix architecture, which is responsible for its ability to communicate genetic instructions and to replicate itself.
The information carried by DNA makes it possible to reliably identify individuals based on their unique genetic characteristics (the exception being identical twins, who have identical DNA). But before DNA testing existed, those attempting to identify individuals and/or familial relationships relied on blood typing and various forms of blood serum (serological) testing from the 1920s through the 1970s.
Then, in 1983, Jeffrey Glassberg filed the first patent covering DNA use in forensics. Shortly afterward, Sir Alec Jeffreys developed an alternate method of DNA profiling, the method first used to assist in a criminal case—confirming the identity of a suspect in the rapes and murders of two teenagers in Leicestershire, England.
Types of DNA Testing
There have been several DNA testing methods developed and used since the 1980s. Several have been retired as new methods emerged that proved to be more sensitive and more accurate. Some of the outdated methods include:
- RFLP analysis – Restriction fragment length polymorphism (RFLP) analysis was the first legitimate method of DNA testing. This analysis was time-consuming and required relatively large samples for testing.
- DQ alpha testing – This method introduced a polymerase chain reaction technique, which required smaller samples for testing. While it was more sensitive than RFLP analysis, it wasn’t as accurate, and its popularity faded quickly.
- AmpFLP analysis – Amplified fragment length polymorphisms (AmpFLP) analysis attempted to combine the best qualities of the RFLP and DQ alpha methods, but it was never widely adopted—abandoned in favor of improving technology. A few places still use it because it is less expensive and easier to employ than modern methods.
Popular current methods of DNA testing include:
- STR analysis – Short tandem repeat (STR) analysis is the preferred (gold standard) method for testing DNA and is widely used in forensic applications. This method is fast and accurate — and requires only a small sample for testing. It can also be used to isolate the Y chromosome for use in paternity identification.
- mtDNA sequencing – Mitochondrial DNA (mtDNA) sequencing analyzes the maternal-line DNA found in cellular mitochondria. While this type of DNA is not unique to individuals, mtDNA sequencing can be used on degraded samples and may be applied to samples that don’t contain autosomal DNA (e.g., hair shaft).
- Rapid DNA – According to the Wikipedia entry on forensic DNA analysis, “Rapid DNA instruments are able to go from a swab to a DNA profile in as little as 90 minutes and eliminate the need for trained scientists to perform the process.” While these tests don’t meet the threshold for national DNA database upload, their speed and ease of use are helpful for law enforcement officials looking for initial indicators of suspects’ possible involvement in crimes.
- Massively parallel sequencing (MPS) – This technique, also known as next-generation sequencing, is still developing. It allows for direct base pair sequencing, which in theory, could even be used to differentiate identical twins.
Limits of DNA Evidence
DNA can be collected from many biological specimens left behind at crime scenes: blood, saliva, sweat, semen, hair, and skin cells, among others. But DNA evidence has limitations, and there are pros and cons to relying on DNA in the criminal justice system.
One issue with DNA is the public misconception that DNA must be present in order to convict someone of a crime. Due to something called the “CSI Effect” (named after the famous set of television shows that focus on solving cases with forensic evidence), many people have a skewed perception of how prevalent DNA at crime scenes actually is. In reality, only a tiny percentage of crime scenes contain usable DNA for investigation, but many people now believe they can’t convict someone unless there is DNA evidence to support the conviction.
Other issues with DNA include fraud, where DNA is planted at a crime scene to frame someone other than the actual perpetrator; a growing backlog of DNA waiting to be tested, which can hold up the judicial system; human error in collecting, handling, or testing DNA, resulting in possible contamination and unreliable results; and privacy concerns depending on how DNA is obtained or cross-referenced through familial connections.
For more information on forensic DNA testing in criminal justice proceedings, visit https://nij.ojp.gov/topics/forensics/forensic-dna.
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