One fish, two fish, red fish, blue fish
What the colors of fish have taught us about human skin color


What is this gene doing?
Remember, genes make proteins, and these proteins come together to make each of us who we are (or each fish who he or she is). In the case of the golden fish, this single change in one gene makes it so that the gene only makes the first part of its normal protein. Over half the protein is missing!
In people, the mutation wasn't so severe. The full protein is made, but the change in the gene just makes one small change in the protein.
How does this protein determine whether fish are dark or golden, or whether people have dark or light skin? We don't know the answer to this yet, but comparing this gene to other known genes gives us a clue.
This gene looks like other genes that make proteins that move sodium, potassium, and calcium across cell membranes (cell membranes act like a wall around the cell, and specialized proteins act like doors to let certain things into and out of the cell).
It is likely that the role of this protein is to move calcium into the cell. Somehow, having more calcium in cells makes more melanin get into the cell. In the golden fish, who are missing most of this protein, not as much calcium gets into the cells. Less calcium means less melanin, and golden-colored fish.
The same idea goes for people- mutant protein means less calcium in the cells, less calcium means less melanin, and less melanin means lighter skin. Of course, this is just a guess based on comparing this gene to other known genes. More work still needs to be done to figure out how all of this really works.
More Information
Does this gene have anything to do with hair color or eye color?
We know that Europeans have many different colors of eyes and hair, whereas most Africans and East Asians have dark hair and dark eyes. Does this gene discovered in zebrafish have anything to do with hair color or eye color?
Interestingly, eye color and hair color are also controlled by the amount of different melanin pigments. But in the case of red hair, it seems that changes in a different gene are responsible (see /ask/ask44). And in the case of blue eyes, changes in at least two other genes are necessary (see http://www.thetech.org/exhibits/online/ugenetics/ask.php?id=162).
But it is still possible that this gene discovered in zebrafish does play a role in eye color and hair color. One idea is that you might need the mutation for lighter skin in order to see the effects of these changes in the genes for red hair and blue eyes.
Why do so many Europeans have this mutation?
So why is it that Europeans nearly all have this mutation, whereas most other people do not? The answer to this is not known.
One possibility is that our need for vitamins played a role. We know that Vitamin D is very important for avoiding bone diseases like rickets. In sunny places, we can make plenty of Vitamin D. But in dark places, such as northern Europe, we can't make Vitamin D as well. Lighter skin helps people make more Vitamin D. For more details and some other ideas, see /ask/ask160.
Whatever the reason, this discovery means that much of the prejudice that has haunted our world for centuries has been due to a single change in one gene. For comparison, siblings have hundreds to thousands of changes between their genes. The truth is that despite our different looks, all humans are >99.9% identical.
Sadly, for years, some people have tried to see whether skin color was related to intelligence. Intelligence is something determined by a combination of MANY genes (and environment). It is extremely unlikely that changes in this gene for skin color have anything to do with intelligence. So in conclusion, race, like beauty, is only skin deep.