It’s not always easy to correctly identify blood at a crime scene.
That was the case in a murder trial that Dr. Bruce McCord, professor within the Department of Chemistry and Biochemistry, served as an expert witness in. A woman was murdered shortly after she went through a divorce, and DNA from her ex-husband was found on her body. But it was hard to tell if the DNA was the result of innocent contact between the two, or if it was incriminating, and came from blood.
“The techniques that we have to detect blood aren’t so sensitive,” McCord says. When the trial completed, he went on a quest to find a better method. “There ought to be tissue-specific markers on the DNA that would be able to differentiate one type from another.”
McCord’s research into that question is part of the burgeoning field of forensic epigenetics, which uses the markers that sit on top of DNA and modify it’s expression, rather than the genetic sequence itself, to gather information that could help identify a suspect in a crime. Forensic scientists and law enforcement agencies around the world think leveraging epigenetics could add key tools to the investigative arsenal. They’re working to develop methods that use this area of study to identify not only the tissue type of DNA that may have been left behind at a crime scene but the age and lifestyle of the person who left it there.
Research is still ongoing, and the technology needs to be tested and validated to ensure it’s effective and accurate. And as the science moves forward, as with any new tool involving genetic information, its ethical concerns must be scrutinized.
All the cells in the body have the same DNA sequence, and that distinct series remains constant throughout an individual’s life. However, how those genes function – what proteins they produce, in what quantities, and when – is something known as gene expression, and it changes, from body part to body part, and in response to all kinds of environmental factors.
For example, blood cells have a different purpose in the body than skin cells do, so different proteins will appear in unique patterns in both cells to help them carry out their specific tasks.
By identifying these patterns, it’s possible to differentiate between the DNA that came from blood, and the genetic coding that came from skin, McCord says. That strategy, he says, has advantages over the current body fluid identification protocols, including that it can be done with DNA sequencing technology already in place at many forensic labs.
McCord and his team are collaborating with the San Fransico Police Department to start to validate their methods.
Going forward, epigenetics might also help predict if a suspect is a smoker, if they drink heavily, or even what their diet is. All of these behaviors leave traces, and it might be possible to predict, say if a person is a long-time vegetarian by looking at their epigenome.
“When someone leaves a sample behind in a violent crime, it’s reasonable to test it and find out as much about that person as we can,” McCord says.
The information isn’t enough to identify a single person – epigenetic markers aren’t fingerprints, and there’s a lot scientists still don’t know about gene expression. But knowing the age range and lifestyle habits of the person that they’re looking for might help law enforcement officers narrow down a suspect pool, in cases where there isn’t a DNA match in a database.
Research is moving ahead quickly, but scientists noted that they’re still working to understand the limits of the methodology: Does it still work on DNA samples that have been degraded in some way, or are only present in small quantities? They also need to make sure that the methods are as effective in all ethnic groups, and that age markers are just as accurate when they’re analyzed from blood as when they’re analyzed from skin.
Read the Popular Science article for the full story.