DNA Fingerprinting and Its Uses
DNA fingerprinting is a molecular genetic method that enables the identification of individuals using hair, blood, or other biological fluids or samples. This is able to be accomplished due to unique patterns (polymorphisms) in their DNA. It is also known as genetic fingerprinting, DNA typing, and DNA profiling.
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.
The Different Methods Used
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 depends on the number of repeating sequences tested and their size.
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 it has a few drawbacks. If samples are not stored quickly and properly, bacteria can attack the cells containing DNA, reducing the accuracy of the results. Another issue is that cells are not visible, so there is no guarantee that DNA will be present after a swab.
Once collected, the samples are processed to extract the DNA, which is then augmented using one of the methods described previously (PCR, RFLP). The DNA is replicated, amplified, cut and separated through these (and other) processes to achieve a more thorough profile (fingerprint) to compare to the other samples.
Fields Where DNA Fingerprinting Is Beneficial
Genetic fingerprinting can be used in criminal forensic investigations. A very small quantity of DNA is reliable enough in identifying individuals involved in a crime. Similarly, DNA fingerprinting can and does exonerate innocent people of crimes—sometimes even crimes committed years ago. DNA fingerprinting can also be used to identify a decomposing body.
DNA fingerprinting can answer the question of the relationship to another person quickly and accurately. In addition to adopted children finding their birth parents or settling paternity suits, DNA fingerprinting has been used to establish a relationship in cases of inheritance.
DNA fingerprinting serves several uses in medicine. One important instance is identifying good genetic matches for organ or marrow donation. Doctors are beginning to use DNA fingerprinting as a tool for designing personalized medical treatments for cancer patients. Moreover, the process has been used to ensure that a tissue sample has been correctly labeled with the patient's name.
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.