I know a little bit about genetics - only really what I learned at school - so know that eye colour is a result of which genes your get from your parents and whether or not they are dominant or recessive. For anyone who doesn't know, I'll briefly explain.
Genes which determine eye colour are either dominant or recessive. Brown is dominant, blue/green is recessive. In order to have blue eyes you need to have two recessive genes from your parents - one from your mother one from your father. (For those of you who know a lot about genetics, I'm aware that it is a bit more complicated than this and that blue and brown don't always adhere to the recessive-dominant rule).
My first son has blue eyes. I have green eyes, his dad has blue eyes. Because one needs two recessive genes to have blue eyes, he obviously got a blue gene from his dad (who can ONLY pass on blue) and a blue gene from me.
My mother has green eyes and my father has brown eyes. Because I ended up with green eyes, it's clear that my father has both a dominant brown gene and a recessive blue, which he passed onto me. My father's father's eyes were brown, his mother's are blue. My first son has blue eyes from my paternal grandmother.
Cool, huh?Other things that are passed on with dominant and recessive genes are: the shape of your earlobes - the gene that makes earlobes hang down a bit are dominant, the gene that makes earlobes attach directly to your head are recessive; hand clasping - if you clasp your hands together as you normally would and your left thumb goes over your right, you have the dominant gene; cleft in the chin- the gene which causes a cleft is dominant (though for some reason, women tend not to be as affected by this).
Whether you can roll your tongue into a tube or not is always talked about as being a simple genetic trait. Recent research, however, shows that it's not quite that simple, as two parents, neither of whom can roll their tongues (recessive gene) can, indeed, have a child who can roll their tongue.
The reason why I'm writing about genetics is that this week I learned something very odd/interesting about my 4 month old son: he has a different ear wax type to me.
For a couple months now, I've been wondering about the strange white, flakey stuff coming out of his ears. I've been wondering if it's shampoo or dried milk. I couldn't figure it out. Then I learned (from Drew http://twitter.com/drew on Twitter) that there are two types of earwax that are determined by dominant or recessive genes.
I have the type of ear wax that I'd guess nearly most of you have: wet: the honey-coloured, moist kind. The gene for 'wet' earwax is dominant. 97-100 of East Asians have dry earwax. South Asians, Central Asians, people form the Pacific Islands, Native Americans and Inuits are split nearly down the middle with 30-50% having dry earwax.
I found it odd that my son has dry earwax as it's a recessive trait. I asked my husband what kind of earwax he has and he looked at me like I was odd. So I said, 'Do you have the honey-like kind? Sticky? Or dry?' I could tell he hadn't realised there were different types of earwax. 'Well, I guess I have dry then.'
So my husband has dry earwax, so he can only pass on the dry earwax recessive gene. Cool. It also means that I have a dry earwax recessive gene kicking around. I do have Native American ancestry, so it's probably come from that. How my husband got dry earwax is very interesting as he, as far as he and his mother (who's doing their family tree) are concerned, is entirely British.
Whoever has passed on the dry earwax gene to my son may be less proud than my grandmother was when I told her my older son had her blue eyes. But you never know!