Previous research proved that a trace of DNA from a crime scene could show someone was there whose natural hair color was red.
New research from Erasmus MC, a teaching hospital in Rotterdam, Netherlands, promises to let detectives distinguish between red, black, brown, dark blond, light blond, and reddish blond hair, all from a tiny sample of DNA, for example from a droplet of blood, saliva or sperm.
These markers for hair color add significantly to the ability of investigators to profile a suspect from DNA left at a crime scene or associated with a victim's body or clothing. Detectives can already use genetic evidence to determine a suspect's gender and predict eye color and age.
"That we are now making it possible to predict different hair colors from DNA represents a major breakthrough," says Manfred Kayser, who led the research team.
Identifying 13 Key Genetic Markers
The advance was made possible by matching the natural hair color of 385 men and women with markers on a dozen genes that were already known to have some influence on hair color. From that massive body of data, the researchers were able to pin down 13 genetic variants on 11 genes that, taken together, allowed them to predict subject's hair color with a high degree of accuracy.
When the researchers combined their results into a statistical model, they were able to correctly predict red hair more than 90 percent of the time, black hair 87 percent of the time, brown and blond more than 80 percent of the time. They were also able to predict whether someone's hair was blond, reddish blond, or dark blond with almost the same degree of accuracy.
The researchers note that they sampled a relatively small number of people. However, previous studies of other genetic markers, for example eye color, have shown that it is possible to generalize results like these to large populations. The authors conclude that the accuracies of their predictions ". . . are unlikely to change drastically when more individuals are added to the hair color model."
Implications of the DNA and Hair Color Study
Several steps remain before these findings will be ready to use in actual criminal investigations. The findings will need to be replicated and refined in other groups, including non-Europeans. When sufficient predictive accuracy has been firmly established in different populations, DNA-based hair color predictions will then be used to tighten the net around suspects or persons of interest.
Ate Kloosterman, a professor in the Department of Human Biological Traces at the Netherlands Forensic Institute, in the Hague, and who was not part of the current research, finds it promising. "This new development results in an important expansion of the future DNA toolkit used by forensic investigators to track down unknown offenders," he says.
Reference: Wojciech Branicki et al., "Model-based prediction of human hair color using DNA variants," Human Genetics (DOI: 10.1007/s00439-010-0939-8).
Robert Adler - Robert Adler is a science and technology reporter and book author. He divides his time between Santa Rosa, California and Oaxaca, ...
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