If a child inherits two recessive genes, say one for blue eyes and one for green eyes, which trait will show?
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The following contains a bit of oversimplifying, but:
It depends. So, genes and DNA aren’t just “the code that says how you are”—they’re actually recipes to make all the proteins in your body. For example, your blood type genes tell your body “Here’s a recipe for the antigens on your red blood cells.” If you have two genes with Recipe A, you have little A antigens on your blood; if you have one A recipe and one B recipe, your body can read those recipes and make both of those antigens, and stick ‘em both on your red blood cells.
Now, eye color is a messy example—I did some reading (https://medlineplus.gov/genetics/understanding/traits/eyecolor/), and it turns out, multiple genes control it! Why? Because we have different recipes that affect it. I’m oversimplifying and tweaking the truth, but imagine recipes kind of like this:
-Do we have a recipe to make melanin, to pigment the iris darker?
-Do we have the recipe for the little protein friends who will move melanin into the iris?
-Do we have a recipe for a protein that says “Make more melanin recipe!” or “Stop making our melanin recipe!”
And so on.
There’s one more component: what’s recessive vs. dominant?
Well. Let’s say there’s a recessive gene that turns your whole body purple—if you have two “p genes”; you’re purple. If you’re PP or Pp, you’re not. Let’s pretend babies are purple in the womb, but most babies have a special protein, “P”, that removes the purple color before they’re born. If I have even one working P recipe, it can remove the purple, and I’m not born purple; but if I have pp from both parents, I didn’t get the purple remover, and I’m born purple. That gene p is recessive, because you need two ps to be purple. (A p recipe means our purple remover is broken or shaped wrong or something.)
Dominant genes are the opposite: babies being not purple is dominant, because one working P recipe removes the purple. So PP AND Pp babies are born their normal color, even if they only have one P recipe.
So, add these things together, and it’s super messy, and I can’t pretend I have an answer! If we could figure out all the processes that determine how an iris has the color it does, and we could tell which genes affected them, and if we knew which were dominant or recessive based on how they work, and we knew which specific “versions” the green- and blue-eyes parents had for all those genes… I don’t think we are 300% sure about eye color yet, at least in the article I read.
But Google says for blue + green it’s just 50-50 blue vs green, so what do I know 🤣 Hope this little rabbit hole makes sense and was somewhat interesting!
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