DNA Fingerprinting and How It Is Used
DNA fingerprinting—also known as genetic fingerprinting, DNA typing, and DNA profiling—is a molecular genetic method that enables identification of individuals using hair, blood, semen, or other biological samples, based on unique patterns (polymorphisms) in their DNA. When first described in 1984 by British scientist Alec Jeffreys, the technique focused on sequences of DNA called mini-satellites that contained repeating patterns with no known function. These sequences are unique to each individual, with the exception of identical twins.
Different DNA fingerprinting methods exist, using either restriction fragment length polymorphism (RFLP), polymerase chain reaction (PCR), or both. Each method targets different repeating polymorphic regions of DNA, including single nucleotide polymorphisms (SNPs) and short tandem repeats (STRs). The odds of identifying an individual correctly depend on the number of repeating sequences tested and their size.
When used for forensic science, DNA fingerprinting makes use of probes that target regions of DNA specific to humans, thus eliminating any possibility of contamination by extraneous DNA from bacteria, plants, insects, or other sources.
Fields Where DNA Fingerprinting Is Beneficial
The most common uses for DNA fingerprinting include:
- Forensics: As most TV watchers know, DNA fingerprinting can be accomplished with a very small quantity of DNA and is a sure-fire way to "finger" a culprit in a crime. Similarly, DNA fingerprinting can and does exonerate innocent people of crimes—sometimes even crimes committed years ago. DNA fingerprinting also can be easily used to identify a decomposing body.
- Noncriminal Identification: Is Joe really Billy's father? DNA fingerprinting can answer that question quickly and accurately. In addition to identifying adoptive children and settling paternity suits, DNA fingerprinting also has been used to establish a relationship in the case of inheritance. More than once, DNA fingerprinting has made it possible for people separated as a result of natural disaster or war to find their children and parents.
- Medicine: DNA fingerprinting serves several uses in medicine. One important instance is identifying good genetic matches for organ or marrow donation. Doctors also are beginning to use DNA fingerprinting as a tool for designing personalized medical treatments for cancer patients. Moreover, DNA fingerprinting has been used to ensure that a tissue sample has been correctly labeled with the right patient's name.
- Agriculture: All living things have DNA, which means that DNA fingerprinting can be used to identify genetically modified plants or plants that are likely to have therapeutic value. It also can be used to prove pedigree in valuable animals such as racehorses.
How DNA Fingerprinting Is Done
For human testing, subjects typically are asked for a DNA sample, which can be supplied as a blood sample or as a swab of tissue from inside the mouth. Neither method is more or less accurate than the other, according to the DNA Diagnostics Center. Patients often prefer mouth swabs because the method is less invasive, but they have a couple of drawbacks. If samples are not stored quickly and properly, bacteria can attack the cells containing DNA. Also, cells are not visible, so there is no guarantee that DNA will be present.
Once obtained and tested, the sample can be used as a tool for treatment development or compared to that of another person to:
- Establish a blood relationship between two people
- Determine whether two people are a good genetic match for medical reasons
- Determine whether a particular individual's DNA matches DNA at a crime scene
- Identify a body
DNA evidence has made a difference in several high-profile cases as its use has become more common since the 1990s. A few examples of such cases follow:
- Illinois Governor George Ryan famously placed a moratorium on executions in 2000 after a review of DNA evidence placed into question the cases against several death row inmates in the state. Illinois completely eliminated the death penalty in 2011.
- In Texas, DNA evidence further validated the case against Ricky McGinn, convicted of raping and murdering his stepdaughter. According to Forensic Outreach, DNA evidence reviewed as part of one of McGinn's appeals confirmed that a hair found on the victim's body belonged to McGinn. McGinn was executed in 2000.
- One of the most famous historical cases impacted by DNA fingerprinting was the murder of Czar Nicholas II and his family following the Russian Revolution in 1917. According to Smithsonian magazine, remains found in 1979 ultimately underwent DNA testing and were confirmed to be members of the czar's family.