Conditions

Can a female get color-blindness from her father's side? My husband and all his brothers are color-blind. Is there a chance my daughter could be too? I don't know of any color-blindness in my side of the family.

-A curious adult from Illinois

December 17, 2004

The quick answer is that yes, a female can get a copy of the gene that leads to colorblindness from her father. In fact, the odds are nearly 100% that she'll get that gene from her dad.

However, to be colorblind, a woman needs to get two copies of the gene that leads to colorblindness -- one from their mom and one from their dad. What this means is that if there is no history of colorblindness in your family, then odds are that your daughter will end up being a carrier for colorblindness.

As a carrier, she'll have one copy of the colorblind gene but not be colorblind herself. She'll also have a 50% chance of passing the gene on to her kids.

It is different for a son who can only get the gene that causes colorblindness from his mother and only needs one copy to be colorblind. These two different situations arise from the fact that the gene that causes colorblindness is found on the X chromosome and is recessive.

As you probably know, boys have an X and a Y chromosome while girls have two X chromosomes -- this is usually how one becomes male or female. Girls need two copies of the faulty gene copy because colorblindness is recessive to having color vision. What this means is that if you have one good copy of the gene that can cause colorblindness, then you won't be colorblind.

So now that we have some background information, let's look specifically at your situation. To make the explanation simpler, we'll use Punnett squares.

Punnett squares are really just a way to organize all the genes and to figure out how likely a combination of genes is. For your current situation, if we assume that you do not carry a colorblindness gene, then we would say you are XX. (This just means you have 2 "normal" X chromosomes, at least as far as colorblindness is concerned.)

We would say your husband is XcY meaning that he has the copy of the gene that causes colorblindness on his X chromosome and a Y chromosome. To make the Punnett square, we'll put your husband's two possible contributions, Xc and Y on the top and your two, X and X on the left side like this:

 Xc Y X X

In each square, we just combine the genes that come together in that square. This'll give the following Punnett square (girls in pink, boys in blue):

 Xc Y X XXc XY X XXc XY

As you can see, all of your daughters, XXc, end up carrying the colorblindness gene. None of your sons carry it because they can only get an X from you. However, since each daughter also carries a good copy of the gene, they are not colorblind themselves but are carriers.

Now if your daughters married men who weren't colorblind, their Punnett square would look like this:

 X Y Xc XcX XcY X XX XY

As you can see, there would be a 1 in 4 or 25% chance for a daughter who is a carrier (XcX), a 25% chance for a colorblind son (XcY), and a 50% chance for a child without the colorblind gene (XX, XY). And if your daughter married a colorblind man? Then it would look like this:

 Xc Y Xc XcXc XcY X XcX XY

Now there would be a 50% chance for a colorblind child (XcXc, XcY), a 25% chance for a daughter who is a carrier (XcX), and a 25% chance for a colorblind-free son (XY). I hope this helps. X-linked genetics can get a bit complex but I always found that the Punnett square helped me a lot.

Are you color blind?