How Common Is Brown Hair Blue Eyes?
- Pieter Maas
Overall, as far as the world population goes, blue eyes and brown hair is pretty rare (4–5% tops).
What nationality has blue eyes and dark hair?
The Healthy Journal – Gluten, Dairy, Sugar Free Recipes, Interviews and Health Articles Meanwhile, black-haired people or people with black hair and blue eyes can be located in any region around the world. Girl with black hair blue eyes or people with black hair and blue eyes naturally are most found in Europe, Middle East, North Africa, and Central Asia, |
Why is dark hair and blue eyes rare?
Is it true that only blonds have blue eyes? Editor’s note (2/13/2021). Some information in this article is outdated:
It describes eye color and hair color as each being determined by a single gene. We now know that both of these are influenced by many different genes. It cites the reason for blonde + blue traveling together is that the “two genes” are on the same chromosome. This is also mostly untrue. Four of the most important genes are located on entirely different chromosomes. For example KITLG is on Chr12, OCA2 is on Chr15, MC1R is on Chr16, and SLC24A4 is on Chr14.
It would be more accurate to say that some genes affect both traits. And that a person’s ancestry affects the chance of inheriting both traits, as described in, No, it isn’t true. My dad has black hair and blue eyes and so do lots of famous people like Gabriel Byrne, Lucy Lawless, and Hugh Grant.
So what was the geneticist talking about? He may have been talking about a couple of things. The first is that blue eyes and blonde hair both come from having less of a pigment called eumelanin. This is just something the two traits have in common – they are not because of the same gene. Image from The genes for each of these traits determines where and how much of the pigment will be made, not if it will be made anywhere in the body.
In other words, the hair color gene determines how much eumelanin will be in your hair and the eye color gene how much will be in the front of your eye. The geneticist may have also been referring to the fact that the two traits usually do travel together.
- Black hair and blue eyes is a much more rare combination than is blonde hair and blue eyes.
- The reason why these two traits are linked is that the genes responsible for hair and eye color happen to be close together on the same chromosomes.
- When genes like these are close together, the traits tend to end up coming in pairs (blonde hair/blue eyes, etc.).
Why would it work that way? To answer this question, we need to go back a step or two. As you might remember, we all have 46 chromosomes that come in pairs. Eggs and sperm each have 23 single chromosomes so that when they combine, you get 23 pairs again.
You might also remember that we all get half our DNA from our mom and half from our dad. A lot of people conclude from this that we each get 23 chromosomes from each parent that are exactly the same as one of the ones our parents had. If this were the case, then of course we’d get the eye and hair color genes together if they’re on the same chromosome – our chromosomes would look exactly like one of our mom’s and one of our dad’s.
For example, for chromosome 15, one would be exactly the same as one of mom’s and the other would be exactly the same as one of dad’s. People often conclude that all the different people we see around us come from the random assignment of parent’s chromosomes to their children.
- In fact, reality is a lot more complicated than this.
- We are all so different because the DNA on our chromosomes gets mixed.
- What really happens is that before getting split up to go into a sperm or egg cell, the chromosomes of each pair swap DNA like mad (except for the Y chromosome in men which has no partner).
This means that the chromosomes you get from your parents are really mixtures of both of their chromosomes. To use our example above, the chromosome 15 you get from your mom is really made up of parts of both of her chromosomes. OK, OK, well and good but what does that have to do with anything? Well, the way the DNA gets mixed up is that big bunches all go at once.
What this means is that the closer two genes are to one another, the more likely they will travel as a pair when DNA is swapped. Why this is true is just a matter of statistics. For genes to get separated, one end of the DNA that is being swapped has to fall between the two genes; otherwise they would travel together on the piece of swapped DNA.
To make this point clearer, try this. On a piece of paper, draw two lines. On one line, put two little boxes right next to each other and on the other, put them at each end of the line like this: Once you’ve drawn these, shut your eyes and put your pencil down on the paper at random.
You should find that the points are almost always between the two faraway genes and rarely between the close genes. This mimics what happens when two genes are linked. The occasional dark hair/blue-eyed person comes from one of these rare DNA swaps that take place between the genes. The swap either took place in one of your ancestors (as would be true for Gabriel Byrne’s kids) or in one of your kids.
I hope this explanation was clearer than that of the other geneticist you were listening to! : Is it true that only blonds have blue eyes?
Can a brown eyed and a blue-eyed person have a blue-eyed child?
Brown eye colour is dominant over blue eye colour. Therefore, for the brown-eyed parents having blue-eyed child, the possibility is that both have heterozygous genotype i.e. Bb. Therefore, from the square below, it is clear that there is a 25% possibility of blue-eyed (bb) child.
Can blue-eyed parents have brown?
Can two parents with blue eyes have a child with brown eyes? Yes, blue-eyed parents can definitely have a child with brown eyes. Or green or hazel eyes for that matter. If you stayed awake during high school biology, you might find this answer surprising.
We were all taught that parents with blue eyes have kids with blue eyes. Every time. This has to do with the fact that blue eyes are supposed to be recessive to brown eyes. This means that if a parent has a brown eye gene, then that parent will have brown eyes. Which makes it impossible for two blue-eyed parents to have a brown-eyed child – they don’t have a brown eye gene to pass on! In fact, this is the model we used for our eye color calculator.* And that we talk about extensively here at Ask a Geneticist.
Blue-eyed parents can have kids with brown eyes. (Image via Shutterstock) Now we aren’t being dishonest or trying to hide anything by presenting this model. It works great most of the time. But as with anything genetic, there are always exceptions. For example, DNA can and does change between generations.
So if a change happened that turned a blue eye color gene into a brown one, then blue-eyed parents could have a brown-eyed child. As you might guess, this sort of thing is pretty rare. Too rare to explain all the exceptions we see with eye color. So something else must be going on. That something is most likely other genes involved in eye color that we don’t know about.
Eye color used to be presented as a fairly simple trait. A big part of the model was the idea that we had an eye color gene that came in two varieties – brown and blue. Geneticists represented the brown version as “B” and the blue version as “b”. The model also said that blue (b) was recessive to brown (B).
This matters because it is an explanation for how brown-eyed parents can have a blue-eyed child. See, we have two copies of each of our genes – one from each biological parent. This means there are three possible combinations for this eye color gene: BB, Bb, and bb. BB is of course brown and in this model, bb would be blue.
Since blue is recessive to brown, Bb people have brown eyes. But they can pass a “b” down to their kids, who might end up with blue eyes. Now eye color is obviously more complicated than this. This model doesn’t explain green eyes for example. Scientists added a second gene to try to explain green eyes but we don’t need to go into that here ( to learn more about the two-gene model).
|Genes||What it Means|
|B b||Brown eyes|
|bb||Not brown eyes|
Again, bb people should not be able to pass on brown eyes to their kids. But we know they can. Which means that this model is incomplete (or wrong). The results I just put into the previous table are theoretical and based on the model I talked about. Here are some actual results I adapted from ‘s website:
|Genes||What it Means in Europeans|
As you can see, the original model holds up pretty well for BB and bb people. Most BB people have brown eyes and most bb people don’t. But the model clearly doesn’t explain the following:
- 1% of bb people have brown eyes
- 1% of BB people have blue eyes (and 14% have green)
- 44% of Bb people do not have brown eyes
The biggest disconnect is with Bb people. Only 56% have brown eyes. If this holds up, I am not sure we can even call blue and green recessive to brown. Whatever the reason, these data give some clues about how two blue-eyed parents might have a brown-eyed child.
- For example, imagine two parents are Bb and have blue eyes.
- They each pass a B down to one of their children.
- That child will be BB and most likely have brown eyes.
- This example uses known data to show how blue-eyed parents might have a child with brown eyes.
- But it doesn’t explain why a Bb person has blue eyes in the first place.
To do this, we need to guess what other genes may be doing. And how they might be affecting the original eye color gene. Going into detail about these possibilities would need more space than I have here! And in the end, the truth is that eye color is a complex trait that we don’t fully understand yet.
Can a brown eyed father and a blue-eyed mother have a blue-eyed child?
A couple’s children can have almost any eye color, even if it does not match those of either parent. Currently it is thought that eye color is determined by about six genes, so you can imagine how inheritance of eye color becomes very complicated. There are some characteristics of various plants or animals that are determined by two simple genes.
- Let’s think about this situation.
- If we say brown is dominant to blue (and we pretend that eye color is decided the way you learned it), someone with brown eyes, like your mom, may be carrying one blue allele and one brown allele (but only the brown shows up).
- She can pass either of these alleles on to her offspring, so in theory, even though brown is dominant, a brown eyed mom and a blue eyed dad could give birth to a blue eyed child.
Now imagine a third green allele, which is dominant to blue, but recessive to brown. If your mother carried the green allele (but only her brown shows up), she could easily pass the green allele on to you (and in terms of probability, would do so 50% of the time), and matched with your dad’s blue allele, you would have green eyes.
- This is a nice way to think about it, but again, eye color is much more complicated, and involves genes that determine the amount of pigment in your eyes, as well as genes that can modify even dominant alleles.
- The wikipedia article on this is written at a pretty advanced level, but it may help explain what is going on with eye color eye color.
Eye image by Laitr Keiows via Wikimedia Commons