Eyes Have It

So, today's is short but interesting.

We've all heard of the Mendelian genetics of eye color:  Big "B" for Brown is dominant to all other eye colors; Little "b" for blue; Little "g" for green; and so on.

But there are actually 8 different genes identified that control eye color.  This is why you can have some icy blue eyes and some baby blue; some black brown and fawn-colored.  It turns out that eye color is produced by a protein in the iris cells of your eyes.  The genes control the amount of protein that is produced in the cells- how often it is recycled in the cells and the shape of the protein.  This protein is produced by melanocytes (colored cells), which are the same melanocytes in your skin (if you have moles, you know ALL about melanocytes and watching for melanoma).  Anyway, large amounts of this "P-Protein" make your iris look brown.  Just like in the skin, this darker pigment is a response to bright UV light; the pigment is a protection for the cell against DNA damage from the UV light.  Cells with damaged DNA can become cancerous, so it makes sense that people living in regions with lots of sun have darker eyes.

It is also interesting that the color is controlled by a protein because this can be affected by your diet or other factors.  My eyes are hazel, but they can have days where they are straight up ochre yellow and other days that they are leaf green and other days that they look brown.  This is probably because of the amount of protein in the irises on a day-to-day basis.  My dad actually 1.75 blue eyes- he's got a little pie wedge of brown in one of them.  I've always thought that was really cool.  It turns out, he's just got a group of cells in his eyes that produce more of this protein than the rest of the cells in his irises.  (This also explains why some days his wedge is bigger than others...hmm)

So, I hope I haven't ruined anyone's genetics lesson plan.  The rules of dominance still hold true...but you have to account for 8 genes, not just a single.