DNA is in every cell in our bodies and carries all the information about how we look and function. For scientists like Dr Mandy Hartley, DNA holds all sorts of fascinating details about us. During her scientific career, Dr Hartley has solved all kinds of DNA mysteries and even set up the forensic laboratories used by Norfolk Constabulary to investigate crimes.
Today, mum of two Mandy helps children learn more about this fascinating field of science through her kid-friendly science workshops and her DNA Detectives children’s books series where kids aged 7-12 learn about DNA science through three engaging adventure stories.
“I have always loved science and even at school I knew this was the career path I wanted to pursue. Children as young as four can learn about DNA through fun, engaging activities and stories.”
Catch Mandy at the Norwich Science Festival at Home on Sunday, 25 October 2020 at 3pm for a fun online workshop where you learn more about how archaeologists use DNA to solve mysteries about the past. Plus you could win a GeoSafari MicroPro Microscope! (Please note this competition has closed.)
In this blog, Mandy tells children more about how detectives solve crimes using DNA.
What is DNA?
DNA is in our cells and is a set of instructions to build us. It holds the information that decides our hair, eye, and skin colour, even whether we like Brussels sprouts or can roll our tongues and much more.
Why do detectives look for DNA?
Everybody’s DNA is different and unique to them (unless you are an identical twin). It’s not just humans who have DNA, all living things have DNA including plants, animals, and micro-organisms. Everything on the inside and outside of your body is covered in cells including your skin, organs, hair, and nails. If we touch something, we will leave some of our cells which are full of DNA behind. If found at a crime scene, DNA can help detectives identify potential suspects.
How is DNA collected?
Let’s imagine a scene – someone has crept into your classroom at school during break time and stolen the sweets on the teacher’s desk. A detective would be tasked with solving the crime and arresting the suspect.
Once the case is reported to the police, Scenes of Crime Officers (SOCOs) are sent to the scene to collect evidence. They will also interview any potential witnesses to build up an idea of what has occurred and identify any potential suspects. Samples of DNA will be taken from those suspects.
The SOCO’s first job is to seal off the crime scene so the evidence is not disturbed or contaminated with other people’s DNA. Evidence will be used to build a story of what happened. It’s important to photograph the scene and the evidence just like we’ve done with our crime scene table below.
Sometimes, the location of the evidence may help us put the story together. It can tell us where the suspect entered the scene and where they left. The pathway between these points needs to be investigated to look for any traces the thief may have left behind.
What do Scenes of Crime Officers wear?
It’s important that Scenes of Crime Officers wear a special forensic overall, gloves, a face mask and foot coverings. This is so we don’t leave our own DNA at a crime scene and contaminate the evidence.
What DNA evidence do investigators look for?
SOCOs look for any cells that could help with their investigation. These include blood, wee, pooh, hair, bogies, saliva, anything that the suspect has worn or touched, nails, and any other fluid produced by the body.
How is DNA evidence collected?
SOCOs look for items they think could hold DNA. This could be a pair of sunglasses, a plaster, a half-eaten lolly, or a hair. When SOCOs find items which they think could have DNA, these are either swabbed at the scene using a swab that looks like a cotton bud or sent to a laboratory.
All items are sealed in evidence bags. These evidence bags are carefully labelled and recorded so they don’t become contaminated, lost, or fall into the wrong hands. SOCOs will also look for other evidence including fingerprints, shoe prints, any fibres left behind from clothing or material used by a suspect.
What happens next?
The items of evidence collected by the scenes of crime officers are sent to the laboratory for analysis by the forensic scientists. Some of the samples like the blood and bogies may be tested to confirm that the sample really is blood or bogies. The tissue might be tested to see where the saliva/bogies are on the tissue. This gives the forensic scientists the best chance of getting DNA from that sample.
The forensic scientists extract DNA from the samples and process them to get a DNA profile. This is a pattern which can be used to identify someone. The scientists compare the unknown DNA profiles found at the crime scene to the DNA profiles from any suspects they may have to see if they get a match. They might also compare the unknown DNA with the national DNA Database which holds the DNA profiles from known criminals.
It is important to realise that just because DNA is found at a crime scene it doesn’t mean someone is guilty. The police need to interview that person to see if they have a good reason for being at the crime scene, or they need to figure out whether someone might have planted their DNA at the scene. They will also look for further evidence.
Forensic scientists will produce a report for the police based on all the forensic evidence they have found and analysed. If there is enough evidence, they will be asked to present this evidence in court in front of a judge and jury. They must present what they believe is the most likely story of what happened at the crime scene given the evidence they have found.
Become a DNA detective
Do you want to learn more about DNA and forensic science? Find out more about Dr Hartley’s DNA Detectives books. Suitable for kids aged 7-12, they make science learning about DNA engaging and fun.
About Dr Mandy Hartley: