Dr. Jeff Salyards, an analyst at Compass Scientific Consulting, visited Caren Peterson’s eighth-grade REACH Physical Science class at Madras Middle School on Dec. 20 to teach students about DNA analysis.
Salyards is the father of one of the students in Peterson’s class. The teacher said at the beginning of each year she asks the parents if they have careers in the areas of the class curriculum.
Salyards is the first parent to visit the class this year.
“Bringing in real-world people makes it more meaningful to them,” Peterson said.
The students were given a mock crime scene involving the “murder” of a plush dog. Peterson and Salyards were included as characters in the scenario.
Salyards told the students the details of the crime scene, which included hearing a dog barking and somebody yelling, a male and female seen leaving the room. Peterson was overheard laughing when Salyards talked about killing dogs.
Salyards added that there weren’t any visible injuries on the dog’s body. Fingerprints, “blood” and a liquid that looked like Gatorade were found at the crime scene.
To solve the crime, the students split into groups to extract DNA from the blood, analyze the fingerprints and examine the liquid.
The students retrieved the DNA from the blood samples on a piece of paper by filtering rubbing alcohol through the blood and into a beaker.
After collecting evidence, the students were able to request a search warrant from a judge – also played by Salyards – to check Peterson’s and Salyards’ fingerprints, and later to retrieve a DNA sample from both.
Once the students had approval, Peterson and Salyards used ink to stamp their fingerprints on a sheet of paper so the students could compare their fingerprints to the ones found at the crime scene. The students found that the fingerprints matched with Salyards, making him the primary suspect.
A phone app that simulated a spectrophotometer – a device that reads the wavelength of light from an object – was used to examine the liquid at the crime scene.
Salyards said he doctored Gatorade with dye so that it appeared normal, but its wavelength actually had higher amounts of green light and less blue when examined with a spectrophotometer.
“It had to be obvious when you use the spectrophotometer, but not to the naked eye,” Salyards said.
Based on that evidence, the students were able to determine that the dog was poisoned by the liquid.
Salyards said he then had the students perform a series of dice rolls to simulate generating DNA from the suspects and the blood at the crime scene. The students used two dice, with each one representing one of the suspect’s parents.
In the scenario, the results of each dice would compare to the chromosomes received from a person’s parents, according to Salyards.
The students would roll the dice and use the resulting numbers to fill out a DNA profile for Peterson. When the students came to Salyards for his DNA profile, he would verbally tell them his numbers, and alter his answers so that only one of his given numbers would match with one number from each dice roll.
For example, if the students rolled a four and a five, Salyards gave a four and a six as his answer.
After collecting the DNA from Salyards and Peterson, the students noticed the former partially matched the data from the crime scene.
“If it almost completely matches, that’s like saying it doesn’t match at all,” Salyards said. “Then they got to have the discovery and I did some didactic questioning with them.”
Salyards had the students examine the profiles and question why his profile would only half-match the genetics found on the scene.
The students then concluded that Salyards’ daughter was the one who killed the plush dog.
According to Salyards, the real-world version of the processes take anywhere from several hours to several days.
“The real challenge from an educational standpoint is you want to make this feel somewhat realistic, but if you make it too realistic it can be a trigger problem where it can be over-emotional. It can be something disgusting,” Salyards said. “But also, if you make it too realistic there is no way middle-schoolers can complete it in a 50-minute time period.”