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DNA Fingerprinting

Fingerprinting has come a long way since the era when Babylonians would press their fingertips into clay as a record of business transactions. Modern fingerprinting has gone beyond just comparing the lines on a person’s finger to comparing DNA. DNA fingerprinting first came about in 1985 when English geneticist Alec Jeffreys discovered that human DNA creates a repeating pattern. Even more impressive, this repeating pattern had elements that were unique to every individual. Dr. Jeffreys used his discovery for human identification testing. In 1988, the courts recognized DNA fingerprinting as evidence in the case Florida v. Tommy Lee Andrews and in 1989 the Federal Bureau of Investigation was using forensic labs for identity testing as well. Today, DNA fingerprinting is offered by over 150 public laboratories and hundreds of thousands of tests are completed each year.


Forensic Identification Process

DNA fingerprinting is a form of forensic identification that is used primarily to identify people. Even though all humans share 99.9% of their DNA sequences, the remaining .01% of sequences is unique enough to differentiate people. In order to use the DNA fingerprinting method, a forensic scientist will need two pieces of DNA to be compared. Because DNA is in every cell of a person’s body, any part of a human’s body including dead skin skills, hair, saliva, and more contain DNA sequences. For example, DNA discovered at the crime scene can be compared to a DNA sample taken from a suspect. A forensic scientist will compare the repeating DNA sequences of the samples and if they are the same, it is a match. These repeat sequences are referred to as variable number of tandem repeats (VNTRs) or microsatellites.


How it’s Done

DNA fingerprinting is often times a voluntary choice. The most accurate method for DNA fingerprinting is for the person being “fingerprinted” to give blood in a medical facility with the assistance of a qualified health care professional. A tight elastic band will be wrapped around the upper arm and a disinfected needle will be used to draw a drop of blood. Babies that are tested as part of a paternity investigation will have blood drawn from their heel rather than their arm. In a case where DNA fingerprinting is being completed on a victim or on evidence from a crime scene, a piece of hair, mucus, saliva, dead skin cells, and more can be used as a DNA sample.

There are different factors which can affect the reliability of testing on a DNA fingerprint sample including the sample size, if the person being identified has had a blood transfusion within three months, and if the sample taken has deteriorated from time.

Highly trained and educated forensic scientists will then run the samples through a series of tests which separate out the microsatellites of the DNA sample. These smaller segments can then be compared to determine if there is a match or if the two samples are related to each other.


Who Uses DNA Fingerprinting

Today, DNA fingerprinting is used for much more than just identifying criminals. DNA fingerprints can also be used to prove a wrongly convicted person’s innocence, identify victims of crime or catastrophic events, prove paternity, match organ donors, and even determine that livestock is of a certain pedigree. In fact, the demand for DNA fingerprinting is high enough that there are several private businesses in the United States and around the world which offer paternity testing based on DNA fingerprinting.

Some of the more unique uses of DNA fingerprinting include identifying September 11th victims, creating a database of people who lost family members in the holocaust so others could identify loved ones separated during the war, and marking souvenirs from the Super Bowl XXXIV and 2000 Summer Olympics with sports stars’ DNA for authenticity.


Ethical Issues with DNA Fingerprinting

The main ethical debate with DNA fingerprinting is privacy. Each state has its own laws, or lack of laws, on how and when to store DNA fingerprinting samples from people who are arrested. The concern is, DNA samples may be held without a person’s consent. If a person is arrested, DNA fingerprinted, and then later found innocent, that person may not want their DNA being stored. Databanks can be hacked or compromised leaving anyone who has been tested at risk of having their privacy compromised.


Additional Resources

Who Done It? DNA Fingerprinting and Forensics – A more in-depth and scientific look at how DNA samples are tested.

How DNA Evidence Works – The entire process of collecting and analyzing DNA evidence.

Explore Forensics – A website dedicated to forensic science with articles, news, expert input, and much more.

Combined DNA Index System – The Federal Bureau of Investigation’s Combined DNA Index System (CODIS) which holds criminal DNA to be shared with crime laboratories around the country.

Forensic Database Policy – Current legislation in the United States and around the world for databanks and DNA fingerprints from the Gordon Thomas Honeywell Organization.

DNA Exonerations – Real life examples of how DNA fingerprinting is used to free innocent people from prison, presented by NPR’s All Things Considered.

The Future of Forensic DNA Testing – The National Institute of Justice’s take on the future of forensic DNA testing.

DNA Fingerprinting in Human Health and Society – In in depth look on how DNA is tested and the different uses of DNA fingerprinting.