One fish, two fish, red fish, blue fish

When we look at a family, it is pretty obvious that skin color is passed on. Dark-skinned parents tend to have dark-skinned babies, light-skinned parents, light-skinned babies. Not always, but usually. You would think that the genetics of something as obvious as this would have been explained years ago. And yet, until just last year, not much was known. What we did know was that skin color, like hair and eye color, is the result of more than one gene. Lots of genes work together to determine our coloring. We also knew of a few changes in genes that could make people have albinism (where they don't really have any pigment). But we didn't really have any idea what genes caused the more garden-variety skin color differences between humans. OK. So by now you are wondering from the title of this article what fish coloring has to do with all of this. Well, you probably have heard that scientists often study other animals to learn things about ourselves. For example, mice and rats are often used to study things from cancer to learning and memory. Just last year, a group of scientists were using fish to study cancer, when they stumbled onto a possible human skin color gene. The fish they were studying are called zebrafish, named after their dark stripes. This dark color is caused by a pigment called melanin. This is the same pigment responsible for dark skin and eye color in humans. A few zebrafish, however, are lighter in color. Scientists named these zebrafish "golden". They knew that the golden coloring was genetic since golden fish usually had golden babies. They figured out that the golden color was caused by a single change in one gene (called a mutation). It turns out that humans have a gene that is similar to the one changed in golden fish. To test whether this gene does the same thing in humans and fish, scientists put the human gene into golden fish. And guess what? The fish had dark stripes and were no longer golden! OK, but does the gene have anything to do with color in people? Actually it looks like it might. When the scientists looked closely at this gene in many different humans, they found a surprising result. Nearly all Africans, Native Americans, and East Asians had the original version of the gene. 93%, to be exact. But in European-American people, 98% had a single change in the middle of the gene. Remember, we each have two copies of most of our genes (one from your mom and one from your dad). The Africans, Native Americans, and East Asians that were studied had two copies of the original version of the gene. The European-Americans looked at had two copies of the mutant gene. What happens when people get only one copy of the gene with this small change? To answer this, researchers looked at people with a mix of African and European ancestors. They found that people with only one copy of the mutant gene had medium-colored skin. So it seems that the same gene that controls the color of zebrafish also plays a role in determining skin color in humans. Of course, skin color genetics are not entirely this simple. For example, most Africans are darker than East Asians, even though both usually have two copies of the original gene without the mutation. But the researchers think that this one change in one gene is responsible for 25-38% of the skin-color difference between Europeans and Africans.