Forensic testing
January 4, 2011
Criminal investigators are just a hair's breadth away from gaining a clearer picture of unknown offenders.
Dutch and Polish researchers have found that DNA from blood, saliva and sperm can be used to identify a perpetrator's probable hair color.
Their study, published Monday in the journal Human Genetics, illustrates the foundation of a DNA test for hair color, which could help police hone in on wanted criminals.
Manfred Kayser of the Erasmus MC University Medical Center in Rotterdam, the Netherlands, who led the study, said the team's findings stand to help investigators with suspect-less criminal cases.
"Currently, DNA profiling is a completely comparative approach," he told Deutsche Welle.
That means investigators might find DNA at the scene, but without a suspect - and his or her DNA - they have no basis for comparison.
But a test for hair color could help forensics teams know who to look for: the study's authors demonstrated that DNA could be used to predict whether someone has red hair with more than 90-percent accuracy, and black hair with nearly 90-percent accuracy.
The team was also over 80-percent accurate in determining whether a person had blond or brown hair.
Researchers developed a model based on 13 genetic markers from 11 genes, using DNA samples collected from nearly 400 Polish Europeans.
Part of a forensic toolkit
It's not the first time Kayser has focused on understanding the biology behind human appearance traits – scientists from Erasmus MC previously led DNA analysis aimed at predicting a person's eye color and age.
"Now, we have provided at least a scientific basis to do this with hair color," Kayser said, describing the latest approach as another tool that forensic investigators might use to refine their search for potential suspects.
Until now, much of the research on genetic markers for hair color had been focused on redheads; red hair is known to be associated with polymorphisms in the MC1R gene.
But by looking at 12 genes and 45 single nucleotide polymorphisms, the team was able to predict other hair colors – and even variations between similar hair colors, such as blond and dark-blond.
Researchers were less accurate when it came to determining whether someone might have brown or blond hair versus red or black tresses.
Yet Kayser said the fact that people's hair color can change over the years – particularly from blonde to brown – might have thrown off the team's predictions.
How useful a DNA test for hair color might be for investigators working suspect-less cases largely depends on geography. Kayser said areas where blond hair is common, like northern Europe, might not find the test as helpful as areas with more diverse populations.
At the crime scene
Meanwhile, the research stands to give investigators more crime-solving options, beyond creating a DNA profile and comparing it to a suspect and a database.
Ate Kloosterman, a scientist at the Netherlands Forensic Institute (NFI) told Deutsche Welle that a DNA test for hair color would help authorities and police get as much objective information on a perpetrator as possible – something that could come in handy for creating composite sketches.
Nevertheless, he predicted such a test wouldn't be available before 2012.
However, there are other limitations: Kloosterman said testing for hair color consumes more DNA than required to create a DNA profile – adding that there's not always ample biological material available at the scene.
Moreover, the latest approach only applies to predicting the color of hair from the head – not other body hair that might be found at the scene of a crime.
There's also the chance that a perpetrator trying to escape arrest might change his or her appearance, by shaving the hair or coloring it.
"In your forensic report, you have to mention those limitations explicitly," Kloosterman said.
Criminals often aren't that clever
But Kayser questioned the likelihood that criminals would think to dye their hair to evade police.
He noted that perpetrators might choose to wear gloves – but the number of offenders who leave fingerprints at crime scenes seems to suggest that many don't.
Ultimately, Kayser said researchers are keen to move beyond group-specific traits like hair and eye color and look toward more individual factors, such as predicting facial morphology.
He noted that scientists are still unsure which genes influence what a person's face looks like.
"The genetic understanding of human appearance is still in its infancy," he wrote in the paper.
Author: Amanda Price
Editor: Cyrus Farivar