Allele

When I was little my mom had a story she would tell me about my eye brows--that they were painted by angels. And it's a pretty adorable story, right? Except these angels were rather ham-handed and dumped their eye brow paint into my eye leaving one of my greyish colored eyes with a brown stain and my eye brows lacking the dark hairy glory of my older sister. I used to gaze longingly at Emily's eyebrows and think of lost dreams that might have been.
Long after my mother's death, this story continues to comfort me. Sometimes as I'm putting on mascara I'll notice the paint stain and feel reassured by the love that would cause a mother to stare into the face of her baby daughter and notice every detail of her eyes. And since this mascara treatment is usually an attempt to get some other person to stare lovingly into my eyes...all I can say is that every bit of reassurance a girl can get is a precious gift.

But a newfound curiosity about eye color has sent me looking* into this phenomena in more depth. (*please appreciate my puns)  According to the internet it's called sectoral heterochromia. If my eye was completely brown instead of just one section it would be called complete heterochromia.

I teach a genetics unit to my 8th graders and we have a lot of fun with punnet squares and the kids love it because 8th graders are pretty egocentric and love talking about themselves. Just like me apparently, since I have a blog.

I'm on spring break and don't have any kids to teach so you are welcome to join my class today.

Quick Genetics Lesson
Every trait or characteristic we have is determined by our genes. Genes are pieces of DNA that each have the instructions for a trait.  There are different versions of a gene, each version is called an allele. Genotype is the combination of genes a person has, phenotype is the traits or characteristics a person has. If your genotype is two different alleles of a gene, whichever allele is dominant will be your trait or your phenotype.
Someone who has two different versions of a gene (or two different alleles) is called heterozygous, while someone with two of the same versions of the gene is called homozygous.

Or just watch this video:



Inherited eye color is easy to oversimplify, thinking that it's as simple as Mendel's pea color. But eye color is caused by several different genes (maybe other factors too). Parents with light colored eyes, tend to have kids with light colored eyes because it's a recessive trait to have light colored eyes. Parents with dark colored eyes can have kids with dark or light colored eyes depending on what genotype the parents had. But a little known fact is that parents with blue eyes can have a baby with brown eyes about 1% of the time; with no milk man involved.

So my Dad has blue eyes and my mom has brown eyes. I don't know if I am heterozygous blue/brown and ended up with blue eyes and only one part of my eye got the brown allele switched on, or if I'm homozygous blue/blue but my eye is damaged? Maybe I'm a chimera and I absorbed a fraternal twin at birth?

Eyes are just weird. Especially when they are featured in music videos with Bonnie Tyler.