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Hair Color

Being a redhead, I thoroughly object to the categorization of our MC1R protein as "not working," as though we are mistakes. We are special, thank you very much. What makes brown right and red a mistake? Maybe this protein is wrong most of the time, and every once in a while it doesn't screw up.

-A curious adult from Pennsylvania

April 20, 2010

This is an incredibly tricky problem that I struggle with any time I write about red hair. Or blue eyes. Or fair skin. Or a host of other recessive traits.

All of these traits have one thing in common. They all happen when a certain gene has a change that causes its protein to not be able to do something it used to.

For example, the MC1R gene has the instructions for making the MC1R protein. This protein does lots of things including turning red pigment into brown.

People with red hair have a version of the MC1R gene that makes a protein that doesn't turn red pigment into brown. These folks have a build up of red pigment and so have red hair.

So how best to talk about this? Clearly the original version of the MC1R gene could turn red pigment into brown. This seems to have been very important for people living in sunny areas near the equator which is where humans started out.

This means that the ancestors of people with red hair made an MC1R protein that could turn red pigment into brown. One of these ancestors then developed a small DNA change in this gene. This change (or mutation) caused the MC1R protein to leave red pigment alone.

People with this change did very well in sun-starved Northern Europe. But not because of the red hair. They did well because of the fair skin that came along with it. If current theories are true, red hair was really just a side effect of the fair skin.

From this it is pretty obvious that the MC1R protein has lost a function it used to have. It could be described as not working properly or even being broken for changing red pigment into brown.

And yet, an MC1R protein that can't turn red pigment into brown was incredibly useful. This version of the protein allowed anyone who had it to survive better in Europe than people with the original version.

So what do I call it? The answers at Ask a Geneticist have to be short or fewer people will read them so I can't have too much explanation. This is why the shorthand of "not working" is so useful.

If the air conditioning (AC) system didn't work anymore in a car, would we call it special? Probably not, we'd call it broken.

But it isn't that simple. If the AC broke in Seattle, you might not even notice it. And the red version of the MC1R gene is even better than this.

Imagine you lived somewhere where gas was 100 dollars a gallon. There it might be an advantage to have a car without AC since it would save on gas. In other words, in that place, an AC that doesn't work would be an advantage. But the AC is still not working.

So how should we talk about the car and its AC? I think I would say that the AC isn't working. I'm not sure this is the best example though because the MC1R protein does more than one thing.

Maybe a better example would be an iPhone. As you know, an iPhone can take pictures, shoot videos, run apps and make calls among other things. Imagine you had an iPhone that could do everything except take pictures. Would you say the camera isn't working? I would.

I would probably say that even if without the camera, everything else worked better. The iPhone still isn't working right even if the apps work faster and there are fewer dropped calls because it can't take pictures anymore.

OK so where are we? I suppose I could say something like:

Some people make an MC1R protein that turns red pigment into brown and some people have one that doesn't. These last people end up with red hair because of a build up of the red pigment.

This is strictly true but a lot of the nuance is lost. Here is what we would say about the iPhone:

Some people have an iPhone that can take pictures and some have one that doesn't. These last people have phones that have more available memory

.Again, strictly true but we've lost the fact that the iPhone can't take pictures because the camera is broken. Not because it was originally built without one.

One more but and I am done...but this doesn't take into account how long ago the change happened.

Imagine that the iPhone with the enhanced capabilities but broken camera inspired two models to be made. One model is a bit slower and has less memory and can take pictures while the other one is faster with more memory but can't take pictures.

To keep the analogy as close to our red hair example as possible, the second model still has the equipment for taking pictures. The camera just doesn't work.

The second model is based on the original broken iPhone but it is now built that way. Then I would certainly describe them as two different models, one with a camera and one without a working camera.

I guess I need to keep thinking about this. I suppose there are times when describing it as not working is very useful. Like when I am talking about the history of red hair or why it is recessive.

But other times it may be best to simply say that people with red hair have an MC1R protein that doesn't turn red pigment into brown. Period, no need for elaboration.

By Dr. Barry Starr

A different gene model or a gene that doesn't work?

Genes that lost functions were important for survival in Northern Europe.

If this iPhone can't take pictures, would you call it broken?