Genetic roulette, anyone?

By Nancy Battick

We’re all victims of genetic roulette. As you know, you get half your genetic code from your mother and half from your father. However, one-half of their genes aren’t passed on to you. Siblings may inherit slightly different genetic mixes. 

But how do you account for things like a red-headed child, the only one in the family? Or a blue-eyed child in a brown-eyed family? Years ago, people would laugh and ask if the milkman was involved. Today there’s no handy milkman to joke about, but the differences can be striking among family members. 

What’s going on? It’s often a matter of so-called recessive and dominant genes.

Fair warning, this explanation is going to be simplified. I couldn’t begin to go into all the random events that are linked to our genes, nor do I consider myself an expert. But here’s the easiest explanation for the differences between siblings. To avoid embarrassing anyone, I’ll use myself as the genetic guinea pig.

My mother had brown eyes, my father blue eyes. In the matter of eye color, the brown-eye gene is dominant and the blue-eye gene is recessive. So, when a couple with these eye colors have a child, the child should have brown eyes. But I have blue eyes. How did that happen? 

Let’s look at genetics. My Dad’s parents both had blue eyes, so he inherited a blue-eye gene and passed that on to me. My Mom’s father had brown eyes, but her mother had blue eyes. That meant Mom inherited a brown-eye gene from her father and a blue-eye gene from her mother. Because the brown-eye gene was dominant, Mom had brown eyes. She was a brown-eyed blonde; Dad was a blue-eyed brunette. 

So, when the genetic roulette wheel turned, I inherited two blue-eye genes, the one from Dad and the recessive gene from Mom. If I’d inherited her brown-eye gene I’d have brown eyes, and if I’d had siblings, they might have had brown eyes.

As for hair color, I began life as a blonde. Both parents were light-haired as youngsters. My hair color changed and by the time I was 12, I was showing definite red highlights and had light chestnut hair until my 30s. No one in Mom’s family had that color hair, but my Dad’s brother and one sister had reddish hair, which I was told was inherited from my paternal grandmother. 

Other traits are linked to genes. Dark hair color is dominant, as is right-handedness, the width of lips, and detached earlobes, among other things. Also linked to dominant genes are some major diseases such as Huntington’s, Marfan syndrome, achondroplasia (dwarfism) and polycystic kidney disease. Recessive genes are linked to cystic fibrosis, sickle cell disease, Tay-Sachs Disease and others.

You can Google (or use your alternate search engine) to learn more about this topic. 

We don’t get to pick our genes, at least not yet. We are truly the product of genetic roulette — and nope, there’s nary a milkman in sight.

Columnist Nancy Battick of Dover-Foxcroft has researched genealogy for over 30 years. She is past president of the Maine Genealogical Society, author of several genealogical articles and co-transcribed the Vital Records of Dover-Foxcroft. Nancy holds an MA in History from UM. Reader emails are welcome at nbattick@roadrunner.com.