Thanks to a mutation in a gene that controls skin pigmentation, the "golden" zebrafish has stripes that are much fainter than the black and white stripes of normal zebrafish. Now researchers have found a similar gene in humans.
Scientists say they've found a gene that seems to partially control skin color. And they say that a small change in the gene could explain why people with European ancestry tend to have different coloring than people of African or Asian descent.
Scientist Keith Cheng says he got drawn into the emotionally charged field of race and genetics because of his interest in a small, tropical fish. "Of course I had trepidations," laughs Cheng, who is a cancer researcher at Penn State College of Medicine in Hershey, Pa. "But my curiosity overwhelmed my trepidation, and this amazing fact that this fish that was found in a pet store might inform us about skin color in a major way was just too much to resist."
Cheng normally studies genetic mutations that cause cancer, with the help of minnows called zebrafish. Usually zebrafish are white with black stripes. But there's also a "golden" variety that has much fainter stripes. Cheng noticed that the difference in skin pigmentation patterns between these two fish varieties seemed to mimic the pigmentation differences seen in people with either dark or light skin. It made Cheng wonder if he could use this fish to explore why people have different skin colors. "How can you not be curious about why an Asian might look different from a Caucasian or look different from an African person?" Cheng asks. "That's very interesting. You look different. Why is that?"
Cheng may have discovered part of the answer, with the help of his lab fish. His team discovered a skin pigmentation gene that, when mutated, causes the "golden" pattern in zebrafish. And then they looked for a similar gene in humans.
In the journal Science, his team reports that people do have a similar gene. In fact, there are two common versions. One showed up in almost all DNA samples taken from small groups of people living in Africa and Asia. The other version appeared in almost all of the people they tested who had European descent.
The researchers also used measurements of light reflection to evaluate skin coloration in a group of people with so-called mixed ancestry. "On average, and I need to point out on average, the variation correlates with skin color," says Cheng. People with the European version of the gene tended to have lighter skin.
Cheng and his colleagues say this information could be useful for studying skin cancer, or for finding new ways of changing skin color that wouldn’t be as damaging as tanning.
But police officers are likely to be interested, too. Already, some officials are testing DNA left at crime scenes to get clues about what the culprit might look like. Tony Frudakis runs DNAPrint Genomics, a Florida-based company that uses gene markers associated with geographic ancestry to give police a general sense of whether someone might look more black or white. In one case, he says, such "DNAWitness" testing helped recently track down a serial killer in Louisiana.
"They had been targeting a Caucasian individual based on faulty eyewitness testimony," says Frudakis. "We showed that the samples found at the crime scene corresponded to someone who was of predominantly sub-Saharan African ancestry. So this sort of changed the profile of who they were looking for." He says his company has done this kind of testing for a wide variety of law-enforcement agencies, including those in places like New York, Chicago and Los Angeles.
Frudakis believes that this method of profiling could be improved by testing genes for more specific features like eye color or height. And he thinks this new gene for skin color is a step towards that goal. Other scientists agree that genes do control a lot of a person's appearance; identical twins are the perfect illustration.
But genetic experts emphasize that this new discovery about skin color is a long way from being able to use gene tests to reconstruct exactly what a person looks like. "Having or not having this particular variant will not allow you to say what shade that person's skin might be, within anything other than very wide limits," says Francis Collins, director of the National Human Genome Research Institute. That's because skin color is controlled by multiple genes.
And Collins also worries that people will confuse skin color with race. "This is most definitely, and let me emphasize this even more, not the gene for race, which is something I've heard a couple people already say when they heard about this result," Collins says. "There is no gene for race."
Collins says the social idea of race depends on all kinds of cues beyond physical appearance and skin color, everything from your neighborhood to your family traditions to your clothes. And that’s what leads Pilar Ossorio, a scientist and lawyer at the University of Wisconsin, to question how useful genetic tests for skin color and ancestry will be for profiling crime suspects.
Consider this, Ossorio says: What if someone with a lot of genes for Native American ancestry and medium-brown skin speaks Spanish and lives in a Hispanic community? "That person could be living in the world as a Hispanic person and the police would probably not connect that Hispanic person with the profile that they got," she says. "We use a lot of things to understand what race someone is, what ethnicity they are, where they fit in our social world." And for most of them, she points out, there is no genetic test.