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A beautiful woman lies slain. Signs of a struggle surround the body. The police have three suspects and one clue: DNA. A sample of the killer’s genetic material has been left at the bloodstained scene, which can destroy the alibi of one suspect, but which one?
 Will it be the victim’s former husband, a star athlete who claims to have been out of town at the time of murder?
Was her current boyfriend the killer? He claims to have been at home when the murder was committed, but cannot corroborate his story.
Or did the pizza delivery boy whom the police have in custody do the deed? He says he was out delivering pizzas miles from the scene, but did he take a deadly detour?
While the suspects wait for their lawyers to arrive, the only people who can solve the crime are an elite team of crime scene investigators — scientists who will take samples of DNA from each suspect and match one to the killer.
These particular crime fighters are not the stars of hit TV show CSI: Crime Scene Investigation, they are some of the country’s top young scientists, members of the National Youth Science Forum, who visited ANU earlier this year. The year 11 students participated in a number of activities showcasing the exciting world of high-level science, including the ‘murder’ investigation laid on by the staff of the School of Biochemistry and Molecular Biology.
Hands-on experience
“To get students interested in science it is so important they are given the opportunity to work in a real laboratory and participate in these types of experiments,” said Ms Dana Sanchez, who organised the event.
“It allows them to see how exciting the field can be and how important it is in our society. This is a fantastic hands-on activity, which demonstrates how DNA profiling could be used to solve a crime.
“Because no two people — except identical twins — have the same DNA, the students can distinguish between the evidence DNA and the innocent parties.”
Using the equipment and techniques found in modern forensic pathology labs, the students were given DNA samples from each of the subjects and the fourth sample taken from the crime scene.
The students treated the samples with a restriction enzyme, which ‘cuts’ the DNA molecules into smaller pieces. The enzyme targets a specific bond in the DNA, which will be at a different place in a different person, producing different sized pieces for different suspects.
Next they incubated the samples at 37C for 20 minutes before adding a small amount of dye and glycerol to the sample. The dye allows scientists to see when the sample has run to the end of the gel, the glycerol helps to weigh the sample down so that it sits in the well of the gel. They then loaded the samples onto an agarose gel.
Finally they used an electrical current to push the DNA through the gel. The gel acts like a series of filters, with large ‘pores’ at the top getting progressively smaller. The length that the DNA molecule travels will depend on the size of the piece, larger pieces will stop at the top of the gel, smaller ones will travel to the end.
DNA evidence
An hour later they viewed the gel under an ultraviolet light, which made the pieces of DNA fluoresce brightly.
So whodunit, you ask?
The damning result (which each young investigator found) blew a huge hole in the former husband’s alibi and would probably be the key piece of evidence that would sentence him to a life behind bars.
For the students, the exercise was a gripping behind-the-scenes demonstration of what professional scientists do and also showed where scriptwriters take liberties with real scientific practice.
“It was a really good experience to see what scientists do hands on,” said student, Luke Howlin.
“It’s fun to see this stuff on TV, but it’s great to do it yourself. It’s good to see how things are really done and see where the line is between fact and fiction — we had to wait three hours for our results, I’m not sure if they do that on CSI.”
Linsey Rankin agreed: “This was fantastic — we wouldn’t have had this opportunity anywhere else.”
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