I am blue-eyed, red-haired, fair-skinned and freckled. I am marrying a brown-eyed, black-haired, brown-skinned Indian man. My friend was joking that I would have a kid with dark skin, blue eyes, red hair and freckles. After thinking about it though, I wonder, what will the skin of my children look like? I am guessing brown, but what about the freckles? I have read that they are a dominant trait. What are the odds of freckles coming through?
-A curious adult from Michigan
September 06, 2007
What a great question! And a surprisingly hard one to answer.
First off, you are right that your kids will probably end up with a skin color darker than yours. But, even though freckles are sometimes dominant, your kids probably won't have them.
This is because your husband most likely has genes that will keep them from showing up. As you may have guessed, skin, hair and eye color is actually pretty complicated.
Out of the 20,000 genes we all share, at least a dozen are involved in pigmentation (the scientific word for coloration). And there are probably more genes that we don't know about yet. All of these genes work together to give a final color.
Some of these genes are stronger than other genes. They can overpower another gene and not let us see its effects.
We also have two copies of most of our genes, one from mom and one from dad. Genes can also come in different versions (called "alleles"). And some of these versions are dominant, or stronger, than others.
There's a whole lot going on here. Let's look at a couple of examples to make all of this clearer. We'll start off with eye color.
Imagine you get a blue eye allele from mom and a brown eye allele from dad. Because brown is dominant over blue, you'll probably end up with brown eyes.
On the other hand, if you have two blue alleles, you'll probably end up with blue eyes. This is because recessive traits will only show up if both copies are of the recessive allele.
But it's not quite that simple. Green eyes, for example, come from a different gene. This gene has a dominant green and a recessive blue version.
It turns out some alleles don't just overpower the other allele of the same gene. Sometimes alleles from one gene can overpower entirely different genes as well!
The dominant brown allele of the first gene can overpower the dominant green allele of the second. So that person can have a dominant green allele in the second gene but still have brown eyes.
Let's back up and think about these two genes as paints. The first gene can paint in brown or blue. The second can paint in green or blue.
If you mix brown paint with green or blue, you get brown eyes. If you don't have brown, but you have green from the second gene, you have green eyes. If you don't have brown or green and have all four blue paints, you'll have blue eyes.
Now let's talk about your child's possible eye color. You probably have only blue alleles in your two eye color genes. But, since blue or green eyes are rare in India, it's likely that your husband has two brown alleles in the first gene. If that's true, then he can only pass on brown alleles for the first gene, and all your children will have brown eyes.
But, what if he has a brown and a blue allele from the first gene? Then your kids could have blue, green, or even hazel eyes. And the chances could be as high as 50% for a color other than brown (click here to learn more).
Believe it or not, eye color is the easy trait. Let's look at skin color and freckles next.
Last year a new pigmentation gene called "golden" was discovered in zebra fish. This gene comes in two alleles -- light and dark. Two copies of the light allele gives zebra fish golden stripes instead of black stripes.
We also have this gene. And it comes in a dark and a light allele too. Almost all people of African, Asian or Native American descent have two copies of the dark allele (click here to learn more).
You can probably guess who has two copies of the light allele. That's right, people of European descent.
Now of course, this gene can't be the whole story. Compare the Japanese and sub-Saharan Africans, for example. Both have two copies of the dark version but there is a big difference in skin tone. Other genes must be involved too.
But let's look at the golden gene for now. In people, it looks like having one copy of each allele gives a skin color somewhere in the middle. This is why biracial kids often have a skin color between their parents.
From this we'd predict that your kids would have a color somewhere between yours and his. But hold on...it might not be so simple in your case. Many people from India have a copy of the dark and the light allele.
What this means is that your child might end up lighter than predicted. And there may even be a small chance for freckles. Let's see why.
You probably carry two light alleles and will pass down only a light allele. Your husband might carry a light and a dark allele. If he carries the light allele and passes that down, your children could have somewhat lighter skin color. If he carries the dark allele and passes that down, your children might have a more medium skin color.
All of this might affect whether your kids end up with freckles too. The main freckle gene in people of European descent is called MC1R.
MC1R actually comes in lots of different alleles. Some of these alleles are pretty strong and can cause freckles if a person has just one copy. Other alleles are not as strong and need two copies to make freckles.
But all of this can only happen with light skin color. People with the dark skin color gene will probably not have freckles even if they have a freckling gene.
Again, let's think about paints. This time we have a skin color paint that comes in a brown (dark) version and a pale (light) version. We also have someone who will splatter on brown spots some of the time to make freckles.
If someone has the brown paint, it doesn't matter if they get splattered or not. The brown spots will be hidden by the brown paint.
But if someone has the pale colored paint, then the spots will show up. The European will have freckles, but the Asian will not (click here to learn a different way that the Chinese can end up with freckles).
At least this is the way we think it works. There are a couple of wrinkles that makes things a bit more complicated.
First off, the freckle versions of the MC1R gene are pretty rare in populations outside of Europe. This means scientists haven't studied a lot of cases of freckles from MC1R combined with the dark version of the golden gene. The lack of MC1R freckles in most of the world's population suggests that most people in the world won't get freckles. But we don't know this for sure. As more people from around the world have kids together, we'll be able to better figure this out.
I know, enough already! Will my kids have freckles? Probably not, but I can think of one way they might if only the golden and the MC1R gene are involved. Imagine your husband has a light version of the skin color gene and you have the kind of freckle gene where you only need one copy to get freckles.
If you pass the freckle gene and your husband passes the light colored gene, then you may end up with a freckled child. Your child will get splattered with brown paint on a pale background.
Notice, though, that I said if these were the only two genes involved. If your husband has another brown skin gene, that would probably dominate over the freckle gene.
And we haven't even tackled hair color yet. We don't really understand it very well but one thing we can say is that your children probably won't have red hair (click here to learn why). Most likely they'll have a light to medium brown color (click here to learn more).
As we discussed, there are lots of genes involved in making us look the way we do. They can all influence skin, hair, and eye color and especially freckles in so many interesting ways. Who thought it would be so complicated?!