Little question about the genetics of blue eyes

October 26, 2020 6:55 PM

I can't figure out how to google this. I have blue eyes and so do both of my parents. But I'm curious about how having recessive genes from both sides affects gene expression.

I know that the genetics of eye color is more complex than shown in middle school Science class punnett square exercises. It's easy to talk about dominant traits vs. recessive traits. But how do recessive traits interact with each other?

Does this mean that my gene expression comes from one parent or a mix of both? For instance, is my shade of blue the result of mixing the blues from my parents or do I get a specific shade from one parent while the other is not expressed? I don't have the same shade of blue as my mother but I do seem to have the same shade as some of my cousins on that side of the family. Not sure the shade of blue from my father as he has passed (I'll have to see if I have good, clear photos of his eyes).

posted by NotTheRedBaron to Science & Nature (5 answers total)

I am not exactly the expert you're looking fir on this but I think it amounts to: to have brown eyes you need a chemical to express in your iris. If you had a brown gene from either parent it would make that chemical. Since you don't have a brown gene you don't get that chemical, thus your eyes are the default colour, which is blue.
posted by How much is that froggie in the window at 7:23 PM on October 26, 2020 [2 favorites]

Eye color is totally fascinating and so much more complicated than recessive vs dominant inheritance. As many as 16 genes are believed involved in eye color and some of these genes are linked (on the same chromosome), which further complicates the issue. These genes seem to affect everything from the basic color to depth of color to the flecks, and then onto how the eye muscles react to light thus affecting other people's perception of the color. And more may be learned as many parts of the world have not yet been studied for this trait.

If you want Punnett square type info, Stanford has an interesting article that lays out the basics of such squares when multiple genes are involved. Popular Science does a very general overview of the gene interactions.

And while it is possible for a particular eye color to seem to be dominant within a family, it is also possible to see what we want to. For instance, my eldest has her father's blue eyes according to people in the grocery store - except when she's next to her maternal cousins who also have blue eyes - then she has the eye color from that side of the family.
posted by beaning at 7:50 PM on October 26, 2020 [3 favorites]

To add to the complexity, eye color can shift in childhood (usually getting darker as melanin builds). My eyes were blue-gray when I was born and have settled on a much lighter shade of brown than anyone in my immediate family. If the light strikes them in a particular way they look kind of yellow.

I may actually be a cat.
posted by basalganglia at 4:56 AM on October 28, 2020 [1 favorite]

I don't have a scientific answer, but I do have brown eyes and was born to two parents with blue eyes. The biology teachers hated me :)
posted by wwartorff at 7:49 PM on October 28, 2020

...but what color are the milkman's eyes? ;)
posted by yeahlikethat at 8:38 PM on October 28, 2020 [1 favorite]