That La Kid

wishin' an' hopin'!

a lesson in genetics and genealogy

on June 12, 2012

Might bore you, but I thought it was fascinating.

This’ll probably play out like a word problem, but anyway… Let me start by laying out some facts:

  • I have Congenital Nystagmus (or involuntary eye movement, acquired in infancy).
  • Gammy’s father (my mother’s mother’s father) had Congenital Nystagmus, which we will call “wiggle eyes” from here on out.
  • My uncle Todd, cousin Cody and cousin Dylan have wiggle eyes.

I’ve never met a person that was not related to me who has wiggle eyes.  I like that.  It’s kind of like a badge of honor that says, “My Great-Grand-dad was a Smith!”  Everyone else that appears to have it in my family is a boy.

According to the smartest person I know, Haley, wiggle eyes are an X Chromosome thing.  If you are a woman, and inherit an X chromosome from each parent, it is unlikely that you will show symptoms, because you’ll probably lean on the X from your dad.  Actually, fifty percent of people who carry wiggle eyes do not show symptoms.

Well, okay.  It’s getting complicated already.  Let me put it this way: it’s kind of like hemophilia.

The gene for hemophilia is unintentionally passed from mothers (XX) to sons (XY) via the X chromosome. A son who inherits a defective X chromosome from his mother does not have a healthy X chromosome to rely on the way daughters (XX) do.

I should have that healthy X, but not only do I have and carry wiggle eyes, I also show symptoms.  So, I’m special.  That is not typical of females.  In fact, if you check out the diagram coming up, you’ll notice a lot of the people in my family who have it are women.  We know they have it because they passed it to their children, but their eyes don’t wiggle.  They don’t show symptoms.

We know Gammy carries wiggle eyes, because her son has it and displays symptoms.  Similarly, we know my aunt, Debbie, carries wiggle eyes because her son Cody has it and displays symptoms.  My mom has it, because her daughter has it and displays symptoms.

In addition Amy, Debbie’s daughter, carries wiggle eyes, because her son Dylan has it and displays symptoms.

So, 3/5 of Gammy’s children definitely have wiggle eyes – though some of their eyes don’t wiggle because you can carry it without presenting symptoms.  Only 1/3 of Gammy’s children that have it display symptoms, because the other two are girls, and have that other X.

Those of us who have wiggle eyes are represented below in red.  The have-nots are blue, because the symptoms are not present in them or any of their children (Adam, Ashley, Tyler and Sunny would all be blue, I just left them off for readability).  Purple people, we’re not sure about.  They don’t present symptoms (their eyes don’t wiggle) but they are women, and we won’t know whether they carry it until we see (or don’t see) it in their children (predominantly in their sons).

I would guess that Joy probably will not end up being a carrier, because it is pretty much 50/50 across the board.  However, since we only know for sure that one of my mom’s three girls has it, it’s likely that either Lindsay or Haley will pass it to their children, but probably not both.  But, you know, it could go either way.

I keep thinking that if I have a boy, he’s a definite wiggle eye, but Ryan and Kyle prove that the boys can escape “the curse”.  If I have more than one kid, though, odds are somebody’s gonna’ get it, even if it’s a girl who just passes it to her son.  The whole point to this is that we found out on Friday that we are having a son.  So, we’ve got a 50/50 shot that my son will not only inherit wiggle eyes but also display symptoms.

Haley, please comment and add all the science info!

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5 responses to “a lesson in genetics and genealogy

  1. Haley Nickel says:

    I think you got all the necessary science. This is a thorough explanation.

  2. Lindsay Kaye says:

    I wanna see Bruce’s little happy!

  3. Mommy says:

    I think you inherited your mom’s “worrier” gene as well. Will you be sharing little happy’s little happy? “No Privacy” ha ha ha

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