-A curious adult from Minnesota
December 16, 2015
Given your parents, you were most likely either going to get your dad’s colorblindness or not be colorblind at all. And it is for the reasons you talk about.
How bad a case of colorblindness you get is often inherited. And in women, you end up with the less severe form of colorblindness that each parent happens to pass to you.
Your dad will pass his colorblindness to you each and every time. But your mom will either pass her severe form or none at all.
This matters here because colorblindness is associated with the X chromosome. And if you have two X’s, the best one for color vision wins out.
This is why men are colorblind more often than women. They have just one X and if it says to be colorblind, they will be colorblind.
The story is very different for women. Because of their two X’s, they are much less likely to be colorblind.
If they have an X that doesn’t lead to colorblindness, it doesn’t matter what the other X says. She won’t be colorblind.
Mild or No Colorblindness
OK so let’s break down your case.
Your mom is not colorblind but one of the more severe forms does run in her family. This means she either has two perfectly fine X’s (in terms of colorblindness) or one of her X’s could lead to colorblindness.
In the second case she would be called a carrier. She can pass on colorblindness but does not have it herself.
Your dad has a mild colorblindness which means his X has it too. And this is his only X.