Fixing Bad Front Page “Facts” with a little OC Science

Hey everybody, I saw the above picture on the front page today, and I wanted to clarify something so that this won’t keep getting spread around. First of all, while this “did you know?” is wrong, it really wasn’t pure shit posting. We USED TO think that eye color acted this way, but recent studies (see linked paper below) have disproven this thought. So the question remains, how IS eye color inherited?

Well, before I start, I need to mention two simple concepts to make sure you don’t get lost in the explanation.

To start, in the VAST majority of cases, humans inherit two copies of a gene (one from each parent). These two traits can interact in TONS of ways or not at all. Here is a list of the most simplistic ways they can be expressed.

Complete Dominance: One is expressed while the other is ignored.
A good example of this is dimples. If you have dimples you either:

Carry one dimple gene (D) and a non-dimple gene (d) making you a mix (Dd)
or
Two dimple genes (DD)

The only way to have NO dimples is to have two non-dimple genes (dd).

Incomplete Dominance: Both of the traits you got from your parents are expressed which results in a mixture of the two.
A good example of this is Pink Roses.

A red rose has two Red genes (RR)
A pink rose has one Red (R) and one White gene (r) making them (Rr)
A white rose has two White genes (rr)

Codominance: Both parent’s traits are expressed independently without mixture.
A good example of this is in blood type. You can have either an A gene (A), a B gene (B), or an O gene (O). O blood type is the absence of a blood type.

If you have the AA combination, you have 100% A on your blood cells.
If you have the AO combination, you have 50% of A on your blood cells.
If you have the OO combination, you have 0% of A or B on your cells.
If you have the BO combination, you have 50% of B on your cells.
If you have the BB combination, you have 100% of B on your cells.
If you have the AB combination, you have 50% A and 50% B on your cells!

As you can see, they are equally expressed with neither showing up more than the other!

So now that you know some basics, let’s talk about what happens in reality and eye color. In reality, one gene rarely codes for one characteristic. Skin color, for instance, has TONS of genes that result in the variety of skin colors we see. Eyes are a similar situation, but they CAN be simplified down a little easier than skin color.

First, there are two major genes for eye color: The Brown Gene and the Green-Hazel-Blue Gene.

The Brown gene is Complete Dominant. This means that if you have the brown trait (B), then you will have brown eyes regardless of your other trait that you inherited.
Example:

Brown Eyes:
Two Brown Traits (BB)
or
One Brown Trait & One Not-Brown Trait (Bb)

Not Brown Eyes:
Two Not-Brown Genes (bb)

The Green-Hazel-Blue gene is Incompletely Dominant. This means that the traits can mix.
Example:

Green Eyes:
Two Green Traits (GG)

Hazel Eyes:
One Blue (g), One Green Trait (Gg)

Blue Eyes:
Two Blue Traits (gg)

IMPORTANT NOTE: Your eye color is NOT determined by the pigment color spectrum like paint! Your eye color is determined by the light color spectrum!

Well, it gets even MORE complicated. The Brown Gene is TOTALLY dominant over the Green-Hazel-Blue gene. This means that if you have EVEN ONE brown trait, then you will have brown eyes.
Example:
BbGG is Brown Eyes, because you have a brown trait.
BBGg is Brown Eyes, because you have a brown trait.
bbGG is NOT Brown Eyes, because you DON’T have a brown trait. If you have two Not-Brown traits THEN (AND ONLY THEN) will you be able to have blue/green/hazel eyes.

If this is still confusing here’s a Flow Chart that I made that might help. I just noticed while uploading that my words got cut off.
Bottom Right Arrow says "Two" on itBottom Left Arrow says "One" on it

Also, the first box should say "Did you inherit a Brown Eye Trait?".... Doh....

A FINAL NOTE: There are other genes that can disrupt this pattern that aren’t well known. Further, the shade of blue/green/brown can vary due to mutations in the gene or environmental factors. This is the simplest eye color can be explained! Hope y’all enjoyed!!

DOG TAX. This is Rosie. She's a little bigger now, but still likes cold stone surfaces.

Sauce: http://www.nature.com/jhg/journal/v56/n1/abs/jhg2010126a.html (as well as a genetics textbook)