DNA evidence may accurately predict an unknown suspect's hair color.
Hair color from blood samples. I'm Bob Hirshon and this is Science Update.
If you watch crime shows, you know that you can get a suspect's DNA from a strand of hair. Now, scientists in the Netherlands have shown that you can also predict a suspect's hair color from their DNA. Forensic scientist Manfred Kayser of Erasmus University Medical Center says that until now, only redheads could be reliably identified by genetic markers.
Unfortunately, the red hair color is very rare in basically all human populations. So, the practical applications, like in forensics, of that red hair color DNA test was always very limited.
For the first time, the team found a way to tell blond from brown hair using DNA, and even distinguish between different shades of those colors. So even when there's no hair at the crime scene, investigators may soon predict the hair color of an unknown suspect from sources like blood or saliva. I'm Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
In ideal circumstances, DNA evidence can be used to put an individual suspect at a crime scene. However, in order to make a person-to-person match, authorities need to compare the crime scene sample to a verified sample of the suspect's DNA—for example, from a database or from a mouth swab taken at the police station.
If, however, there's no known suspect at at the start of the investigation, then DNA evidence can be used only to narrow down the possibilities. For example, a DNA sample clearly reveals the suspect's sex, and can indicate whether the suspect was biologically related to the victim. What scientists would like to move towards, however, is using DNA like a police sketch artist, to help create a picture of what the perpetrator might look like.
As you heard, scientists have been able to identify red-haired people from their DNA for some time. However, this isn't very useful in criminal investigations, since red hair is found almost exclusively in people of Northern European descent, and is rare even within that group. So the chances that your suspect will turn out to be a redhead are pretty small, and finding out that your suspect isn't a redhead eliminates very few people from consideration.
By focusing on 11 different genes with 13 hair color-related genetic markers (bits of DNA associated with a particular trait), Kayser's team developed a significantly accurate, though not perfect, way to identify more hair colors. Their technique could identify red and black hair with 90 percent accuracy, and brown or blond hair with 80 percent accuracy. Kayser suspects that it may be a little harder to tell blond from brown hair because some people have blond hair when they're younger, but darker hair as adults. Their technique could also distinguish between different shades of blond hair, and different shades of red.
Although the technique isn't 100 percent accurate, Kayser says it's certainly good enough to be included as one of many clues in an investigation. He says the test would have to be simplified to be used easily by investigative agencies. He also notes that their results apply only to hair on the head, and not hair color anywhere else on the body. His lab is also working on ways to predict eye color from DNA samples.
Now try and answer these questions:
- When would it be useful to predict a suspect's hair color from a DNA sample? When would it be unnecessary?
- Why are tests like these useful if they aren't 100 percent accurate?
- What are some ethical questions involved in using DNA evidence to identify unknown suspects?
In the Science NetLinks lesson Cracking the Genetic Code, students research and write a feature article on the Human Genome Project. They come to understand what the knowledge of DNA can tell us about ourselves and other organisms and species.
In the Science NetLinks lesson Extracting DNA, students develop understanding of DNA by modeling the process of DNA extraction.