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Hair Color

My husband and I were wondering about the odds of making a red-headed child. He has very rich, very red hair. I on the other hand have had many hair colors and don't know what my genes are doing. From Birth to age 3, I had bright red hair. From about age 4 to 7 I had bleach blonde hair. After age 7 it turned sort of a dirty blonde, and has been ever since. My Dad had red hair till he was 30 years old then it turned dark brown. We are also very freckled people who sunburn very easily. I don't understand how hair color can change like that, and what genes I'm really carrying. If it helps, my mother has light brown hair and some freckles. Also, both my parents have green eyes, as do I. I hope you can at least explain the changing hair color phenomenon.

-A curious adult from Florida

July 8, 2005

The odds are pretty good for having a redhead. Something around 50% or greater, I'd guess. As for your hair color changes, most likely different hair color genes turned on and off in your first seven years of life.

An important point often overlooked in genetics is that for a gene to have an effect, it needs to be working. When a gene isn't working, it is like it isn't even there.

A gene might not be working for a variety of reasons. Maybe it has a mutation or a change in its DNA. We can think of this as a broken gene. When this is the case, a trait tends to be pretty stable -- blue eyes stay blue.

Or maybe it's not working because it is shut off. To do something, a gene must be read by the machinery in a cell. Sometimes there are things in our cells that keep a gene from being read. When that something goes away, a gene can then get turned on.

When a gene is off instead of broken, traits can be less stable -- blue eyes can change color later in life. Or red hair can change to light blonde and then change to a darker blonde.

Genes turning on and off over time is pretty common. Examples include all the genes that get turned on when we hit puberty or the gene that lets us digest lactose, a sugar in milk. Many adults are lactose intolerant because this gene shuts off over time.

Now, what specifically might have happened in your case? To understand this, we need to dig a bit deeper into hair color genetics.

Red hair has the simplest genetics of all the hair colors. The most common way red hair happens is when both copies of a gene called MC1R are either not working or are off. (Remember, we have 2 copies of most of our genes, one from mom and one from dad.)

You started out with red hair which means that both of your MC1R gene copies weren't working for some reason. Sometime around your 4th birthday, one or both copies of your MC1R gene turned on.

Once your MC1R gene(s) started working, your hair color reverted back to what it would have been with a working MC1R gene. Why was your hair blonde at this point? Because it had very little pigment.

The amount of pigment in your hair determines the range of colors from blonde to black. Blonde hair has very little pigment, black hair has a lot.

Of course genes determine how much pigment is in your hair. There are many hair color genes, each of which can be either working or not. If a hair color gene is on, then it contributes a bit of pigment to your hair. So, the more hair color genes that are on, the darker your hair.

When your MC1R gene turned back on, you had very few other hair color genes on so you ended up with blonde hair. Then, as is pretty common, when you got older some of these genes turned on. And so your hair got darker.

So now that we have all of that, why did I think there was a 50% chance for a redhead? From what you've told me, you most likely have a single working copy of the MC1R gene. I am guessing this because people who freckle and sunburn easily often have only one working copy of this gene.

If this is the case, then half the time you will pass down a working MC1R gene and half the time one that doesn't work. Since your husband has red hair, neither of his copies of MC1R is working. This means he will always pass down a broken MC1R gene.

So together, the two of you have a 50% chance of passing down two MC1R genes that will lead to red hair. And the odds may be even higher.

This is because we don't know why your hair started out red. It may be that in your eggs, all the MC1R genes are off. If that is the case, then all your kids may end up with red hair.

And then, depending on what turned one of your MC1R genes back on, some of your kids may lose their red hair. Since this hair color change runs in your family, it may be that they'll need to have a second gene that'll turn on the MC1R gene later in life. Or all of your kids might keep their red hair. Or...

As you can see, genetics can get complicated pretty quickly. Traits aren't necessarily stable so it can be hard to predict what our future kids will look like. But, there is probably a 50% or greater chance that your kids will have red hair.

By Dr. Barry Starr



Lactose intolerance happens when a gene shuts off.