Eye color is much more complicated than is usually taught in high school (or presented in The Tech’s eye color calculator). There we learn that two genes influence eye color.
One gene comes in two versions, brown (B) and blue (b). The other gene comes in green (G) and blue (b). All eye color and inheritance was thought to be explained by this simple model. Except of course for the fact that it is obviously incomplete.
The model cannot, for example, explain how blue eyed parents can have a brown eyed child. Yet this can and does happen (although it isn’t common).
New research shows that the first gene is actually two separate genes, OCA2 and HERC2. In other words, there are two ways to end up with blue eyes.
Normally this wouldn’t be enough to explain how blue eyed parents can have a brown eyed child. Because of how eye color works (see below), if one gene can cause brown eyes, it would dominate over another that causes blue. In fact, that is what happens with green eyes in the older model. The brown gene dominates over the green one resulting in brown eyes.
The reason these two genes can explain darker eyed kids with lighter eyed parents is that the two genes need each other to work. And that the blue versions are broken genes. Here is what things look like:
