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This article was first published on January 23, 2012 and was reviewed and updated by the CurioCity team in September 2017.

Some Hollywood TV shows and movies would have you believe that DNA identification is the be-all and end-all of crime scene investigation, a guaranteed science trick which will solve the crime by the end of the episode. This isn't quite the case. Still, DNA identification can be extremely useful in solving mysteries.

The History

DNA is a molecule which determines biological characteristics. DNA is inherited, with half of yours coming from your mother and the other half from your father. That’s why DNA can be used in paternity tests to identify biological parents.

Did you know? The majority of every person's DNA is identical (99.9%); however, a tiny part of each person's DNA (0.1%) is unique to themselves. That’s what gives each of us our different physical characteristics.

Passing along characteristics was first studied and made famous by Gregor Mendel, who studied pea plants and saw what characteristics were passed along through the generations. Although Mendel demonstrated that living organisms could pass traits on to their offspring, it wasn’t until nearly years later Watson & Crick, with the help of Franklin and Wilkins, determined the proper structure of DNA. It was not until the 1980s that geneticists showed that DNA was unique to each person, just like fingerprints. And DNA fingerprinting was born.

Did you know? DNA fingerprinting was first used to clear one suspect and identify a new different one in a 1985 rape case in England.

The Science

The technical name for DNA fingerprinting is DNA profiling. Here is how it works:

Police collect DNA samples from a crime scene. These samples could include saliva, blood, semen, skin, hair, or tears.

The DNA fragments are analyzed in a process called electrophoresis. Electrophoresis separates DNA strands on a gel using an electric current.

Once police have a suspect, they’ll also analyze their DNA fragments using electrophoresis.

The two DNA samples are then compared to see if they match.

The Controversy

DNA fingerprinting was controversial when it first appeared. Back then, the standards for analyzing DNA weren’t clear, meaning that there was a chance that some tests could possibly give different results. There was no doubt about the science, just human error.

Today, unlike what movies and TV would have you believe, DNA is not the only way to catch criminals. Often, there is no DNA found at the scene of the crime. Other times, the sample has been slightly there - think of smudged fingerprints, for example.  

Also, DNA processing takes a long amount of time, and facilities are not always available to smaller communities. So while DNA can be a very effective tool for finding and prosecuting criminals, it’s not always possible to use it.

There’s also a thing called the CSI effect. This is based on the popular TV series from the mid-2000s. During a trial, jury members expect DNA evidence. When there is no DNA evidence in a case, juries tend to believe the evidence against a suspect is limited. Meanwhile, when there is DNA evidence, juries believe that the evidence is very strong.

This effect can cause problems. Sometimes, DNA evidence simply isn’t available. Also, just because a person's DNA is at the scene of a crime, it doesn’t necessarily mean they committed that crime. It simply means they were at that location at some point in time.

So, DNA evidence is a handy tool when available. However, it can’t replace the detective skills a person needs to put a case against a suspect together.  

Glossary

DNA stands for deoxyribonucleic acid and is our blue print. In other words, DNA is what makes you uniquely you!

Geneticist is a scientist that studies genetics.

Learn More!

Fun DNA Exercise! (2017)
Newton’s Apple

DNA Day
CurioCity

This answer was researched and written by Rebecca Spring, an environmentalist with an interest in genetics and the history of science.

Rebecca Spring

I am a science communication graduate. I work at an environmental organization in Toronto. In my free time, I am learning Spanish so I can travel and work in South America.

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