{"id":352279,"date":"2024-07-09T15:30:00","date_gmt":"2024-07-09T20:30:00","guid":{"rendered":"https:\/\/content.findlaw-admin.com\/ability-law\/criminal\/criminal-procedure\/how-dna-evidence-works.html"},"modified":"2024-07-09T15:30:00","modified_gmt":"2024-07-09T20:30:00","slug":"how-dna-evidence-works","status":"publish","type":"page","link":"https:\/\/www.findlaw.com\/criminal\/criminal-procedure\/how-dna-evidence-works.html","title":{"rendered":"How DNA Evidence Works"},"content":{"rendered":"\n
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How DNA Evidence Works<\/h1>\n
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\n By Sarah Williams, J.D.<\/a> | Legally reviewed by Melissa Bender, Esq.<\/a>\n | Last reviewed\n
\n \n <\/i>\n Legally Reviewed\n <\/summary>\n\n
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This article has been written and reviewed for legal accuracy, clarity, and style by FindLaw\u2019s team of legal writers and attorneys<\/a> and in accordance with our editorial standards<\/a>.<\/em><\/p>\n\n <\/div>\n <\/details>\n\n

\n \n <\/i>\n Fact-Checked\n <\/summary>\n\n
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The last updated date refers to the last time this article was reviewed by FindLaw or one of our contributing authors<\/a>. We make every effort to keep our articles updated. For information regarding a specific legal issue affecting you, please contact an attorney in your area<\/a>.<\/em><\/p>\n\n <\/div>\n <\/details>\n<\/section>\n

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Law enforcement agencies use DNA evidence to narrow criminal suspects down to a few possibilities. DNA technology is highly accurate as long as the chain of custody is not broken. This means DNA is valid if it’s handled and analyzed correctly.<\/p>\n\n <\/div>\n\n

DNA samples and DNA testing involve comparing biological material against other specimens. This creates a profile to identify a unique individual in a criminal case.
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DNA evidence is one of the best examples of how technology has altered the criminal justice system. Particularly, it can help exonerate the falsely convicted<\/a>.<\/p>\r\n

This article explores the use of DNA databases in criminal investigations and trials.<\/p>\r\n

What Is DNA?<\/h2>\r\n

DNA (deoxyribonucleic acid) is a basic building block of life. The information encoded in an organism’s DNA acts as a blueprint for the organism’s biological development and functioning.<\/p>\r\n

DNA exists in the cells of all living organisms. By testing the DNA found in a person’s cell, scientists can develop a DNA profile for them. Only one-tenth<\/a> of 1% of human DNA differs from one person to the next. Although estimates vary, forensic DNA analysis is roughly 95% accurate.<\/p>\r\n

But the development of forensic DNA evidence<\/a> and DNA profiling didn’t exist until the mid-1980s. Scientists discovered that certain areas of the DNA strand contain patterns that repeat many times. They developed a test to measure the variation in the length of these repetitions. The number of these repetitions varies between people (except identical twins with the same DNA). The test developed to measure repetitions became known as restriction fragment length polymorphism<\/a> (RFLP).<\/p>\r\n

RFLP is an accurate and reliable test, but it requires a relatively large amount of DNA to work. Laboratories now use tests based on the polymerase chain reaction<\/a> (PCR) method, which allows testing on tiny amounts of DNA from biological samples.<\/p>\r\n

What Is DNA Evidence?<\/h2>\r\n

Similar to fingerprints, each individual has a unique DNA profile. There is an exception for identical twins, who share the same genetic code. Unlike fingerprints, only a minuscule amount of genetic material is needed to identify a suspect for a criminal trial.<\/p>\r\n

One of the most reliable forms of evidence in many criminal cases is in our genes. A person’s DNA (deoxyribonucleic acid) is biological evidence that can be analyzed in crime laboratories. DNA evidence can be collected from blood, hair, skin cells, and other bodily substances. It can even be used to solve old crimes that occurred prior to the development of DNA-testing technology.<\/p>\r\n

This article provides a basic overview of DNA as a source of evidence<\/a> in the criminal justice system.<\/p>\r\n

Forensic DNA Evidence: A Brief History<\/h2>\r\n

The science of DNA testing was developed in 1985 by British scientist Alec Jeffreys. Genetic evidence was first tested by a forensic laboratory using his method one year later to solve a double homicide in England. It allowed law enforcement officers to link the suspect to other previously unsolved rapes and murders in the area. In 1987, a Florida rapist became the first criminal defendant in the United States to be convicted through DNA.<\/p>\r\n

As DNA became the gold standard for identifying criminal suspects, law enforcement agencies took note. The FBI and police departments throughout the U.S. started assembling DNA databases<\/a> such as the Combined DNA Index System (CODIS). <\/p>\r\n

In addition, sex offenders in all states are now required to submit DNA samples to their local police department. Many states make use of DNA evidence even in criminal charges involving misdemeanors, although many crime labs are overwhelmed with backlogs of genetic samples and may be unable to process them in a timely fashion.<\/p>\r\n

Other Uses of Genetic Evidence<\/h2>\r\n

Genetic material preserved in evidence lockers has many applications. In addition to criminal investigations, DNA analysis can also be used to exonerate wrongly accused individuals<\/a>. That includes those who were victims of wrongful convictions for violent crimes like sexual assault. This is important for those convicted solely on the basis of eyewitness testimony, which is not always reliable. More than 575 people have been exonerated<\/a> through post-conviction DNA tests.<\/p>\r\n

DNA court orders can also be used to determine paternity in child support<\/a> cases. In the world of forensic sciences, DNA technology can also be used to:<\/p>\r\n