Yvette's Inner Geek Blog

Continuing yesterday’s topic of eyes and genetics.

My maternal grandfather was red-green colorblind, as was his brother. I don’t know if either of his parents were colorblind, but since the gene expresses itself only on the X chromosome* and is therefore only inheritable to men via their mothers, my great-grandmother was a carrier of the gene if not colorblind herself. If she were only a carrier, each of her boys had a 50% chance of inheriting the gene.

Genetic probability is like Rosencrantz and Guildenstern in my family: absurd, but not impossible. My grandfather had nine daughters and my great-uncle had four daughters.

So all of my aunts and their first cousins inherited a color-deficient X chromosome from their fathers. At least two of my male first cousins are colorblind, and who knows how many of us females are carrying the gene since none of us have children yet. But it turns out that my great-uncle’s wife was also a carrier of the gene—and one of her four daughters is colorblind (0.5% incidence rate in women). Both of her sons are colorblind.

Another thing I find very interesting in my family is the statistically high number of colorblind men whom my aunts have married. If only 5-8% of men in the general population are colorblind, it’s absurd, but not impossible, that a third of my married-into-the-family uncles are colorblind. (Maybe it has something to do with a genetically predisposed attraction to men who wear mismatched socks.)

I wonder if there’s a correlation between color blindness and eye color? It seems like there should be some sort of science already done on that sort of thing. I’m guessing not, since eye color is determined by a completely different set of genes. Wouldn’t it’s be cool, though, if people who were colorblind had, ironically, one green eye and one red eye? Yes, I’m also fascinated by heterochromia (each eye a different color: think David Bowie), though that doesn’t run in the family. Well, technically my hazel eyes are an example of central heterochromia (two different colors in the same iris) but that’s just not as cool. (Well, I do have a trick lazy eye that’s kind of cool. I can control it and easily weird out Ben anytime I please. Heh heh.)

So what have I learned from all of this? That I am easily fascinated.

Semi-related: At the next family reunion, I want to take close-up photos of everyone’s eyes (blood-related and not), then ask people to guess whose eyes they all are. It’ll be interesting to see how similar (or different?) they all look.

*You can learn more about the details and probability of inheritance from Causes and Incidences of Colorblindness