A strand of hair or a piece of skin can help prove someone was at the scene of a crime — but UA researchers are moving way beyond that.
The scientists say their research could provide law-enforcement agencies with a physical description of a suspect who is still at large, using DNA samples recovered at a scene.
After looking at the hair, skin and eye color of about 1,000 University of Arizona students, then comparing the readings to the students' genetic makeup, the researchers have been able to find a way to predict what people will look like, in terms of eye, skin and hair color.
"There are cases when a blood or semen sample is left at a crime scene and there are no witnesses," said Murray Brilliant, a University of Arizona professor at the Steele Children's Research Center. "This can help in an investigative way."
Brilliant leads a research team that studies genetic disorders that affect people's skin color, such as albinism.
While studying the genes responsible for skin pigment disorders, the team found that three or four among about 30,000 total genes control much of a person's pigmentation, which influence skin, hair and eye color.
By analyzing and identifying variations in those genes, the researchers found that looking at someone's DNA sequence could allow them to make accurate predictions about that person's appearance.
In other words, they found that a small change in a few genes could cause someone's hair to be brown or blond, or their eyes to be blue or green.
"We're trying to understand how human beings make pigment," Brilliant said. "And there's a parallel interest in the forensic community."
If a DNA sample is found at a crime scene through hair, semen or saliva, forensic scientists could look at Brilliant's models and make predictions about what the person who left the evidence may look like.
With a DNA sample, the team is currently able to predict someone's hair color to about 80 percent accuracy, eye color to about 75 percent accuracy and skin color to about 50 percent accuracy — percentages the researchers say are relatively accurate considering the broad range of color each of those physical attributes has.
To find the closest match, the researchers compared their subjects' features to hundreds of different eye colors and shades and the 11 skin tones on a dermatological scale. They also found precise levels of melanin — the compounds that affect color — in hair.
Although Brilliant said his laboratory is most interested in researching pigment disorders, he predicts his team's work will have strong implications for forensic scientists.
In fact, the five-year, $680,000 study by the UA team was funded by the U.S. Justice Department with those applications in mind.
Brilliant said that although the technology won't provide law enforcement with an exact image of a crime suspect, it could provide a pretty good idea of what the person might look like. It also could help law-enforcement agencies learn more about unidentified missing victims.
One expert who first heard of the technology on Monday said it could be helpful.
"If characteristics like hair color, eye color and ancestry are being predicted, then it's a very welcomed aid, assuming that the technology is reliable," said Bruce Anderson, a UA adjunct assistant professor who has taught courses on forensics and works at the Pima County Office of the Medical Examiner-Forensic Science Center.
Currently, the technology is too vague to be used as evidence, but Brilliant thinks it could be used as an "investigative tool," narrowing a pool of suspects.
"It's not 100 percent, but 80 percent is more accurate than an eyewitness," he said.
While DNA analyses of this nature have been used previously by law-enforcement agencies on a limited basis, Brilliant said those analyses had a more limited scope, such as only looking at race.
"This is broader," he said, adding that UA students were a perfect pool to find test subjects because of their diversity.
Because the country is a melting pot of ethnicities, it's important to test different types of people, Brilliant said.
"This has been studied in the genes of individuals, but this is the first time it's all been put together, looking across different populations independent of race and ethnicity."
Brilliant said many other laboratories around the world are working on similar research, looking at DNA to determine someone's height, body type and especially behavior.
The statistics show a significant association with genes and physical traits, said Robert Valenzuela, a UA student who conducted the statistical analysis in the study for his doctoral dissertation.
"We feel comfortable with the statistical power," he said.
On StarNet: To learn more about crime in Tucson, check out the StarNet Police Beat blog at go.azstarnet.com/policebeat
How They Did It
First, the research team measured the skin tone, hair color and eye color of about 1,000 University of Arizona students.
Then it took a sample of the students' DNA by swabbing their saliva.
Once all the samples were collected, the team looked at the genes known to affect a person's appearance, in terms of pigment.
Through statistical analyses, the team was able to make connections and see patterns between the students' genetic data and their appearances.