A case of crime in the genes

DNA, or deoxyribonucleic acid, is a chemical found in practically every cell in our body. Within our DNA, we have about 30,000 genes and these genes contain a code or blueprint for things like our eye colour and hair colour. Every person’s DNA is unique.

All forms of life have DNA, including plants, animals and even viruses. DNA can be used to identify the parents of a child, and it has been used to determine the genetic origin of archaeological finds, such as a 500 year-old Peruvian Ice Maiden, discovered by mountain climbers in 1995.

DNA is also an important source of evidence for police forces. Dr Dorothy Ramsbottom is a forensic scientist and she works in the DNA section at Garda Headquarters in Dublin. She analyses DNA as evidence and in her work, she has tested the DNA of hundreds of suspects.

Unique

Dorothy says that as well as the DNA that contains genetic information like our eye and hair colour, we have other DNA in our cells. “We have a huge amount of non-functioning DNA and it’s this non-functioning DNA that doesn’t code for anything, that is unique to everybody,” she says.

At a crime scene, DNA can be found either in blood (if the criminal has cut themselves), skin cells, hair or saliva. Scientists can analyse the blood type and determine the hair or skin colour from material they find at a crime scene, but these pieces of evidence might not be specific enough to link a particular person with the crime scene.

If the investigation team also has a DNA match, it is much easier to link the suspect with the evidence. Scientists investigating the scene will take a sample of DNA from the scene, and bring it back to the forensics laboratory to analyse it.

Profile

“We can generate a genetic DNA profile which is like a unique genetic barcode for everybody.
Then we can compare these to find out if there’s a match or not,” says Dorothy.

The genetic barcode is like a chart with lots of numbers and scientists use these numbers to compare two pieces of DNA.

The result could exclude a suspect from an investigation. Or it could indicate the likelihood that a suspect was at a crime scene. Either way, it is another way in which science helps investigate crime.

Learn more:

Find out more about what DNA is

Read how DNA is used in forensics

Read about the DNA database in Iceland

See amazing photos of DNA at the Online Exhibits section of the understanding genetics website