Craig asks:

>I tried to find a genetics chatroom but I thought maybe someone could
>answer me. My son who is 2 months old has one brown eye and one
>green-grey eye. It turns out my wife's aunt has the same thing. Is
>this common? This gene would probably be recessive, so does this mean
>I'm also a carrier? I have brown eyes and my wife has green eyes. My
>son's twin sister has two lighter brown eyes.
>
>I think David Bowie has this and I heard Alexander the Great also had
>this. Any other famous people?

This is a recurring question here on this newsgroup. Enclosed below is how I
answered the question approximately four years ago:

======================================

From: Wirt Atmar (wirtatmar{at}aol.com)
Subject: Re: Human eye -- weird pigmentation 
Newsgroups: sci.bio.evolution
Date: 2000/01/05 

Louann Miller asks:

>Just a quick question, probably not controversial in any way but an
>oddity I've been wondering about over time.
>
>I had a college classmate whose left eye was two different colors. The
>iris was divided into two distinct half-circle shapes, blue on one side
>and light brown on the other. The dividing line (vertical) was sort of
>greenish. Her right eye was the same shade of blue as the blue half of
>her left eye.
>
>She said it had always been like that, it didn't hurt, and she didn't
>have any vision problems. I didn't think to ask if anyone else in the
>family had it. It was weird enough to be memorable. I've never met or
>heard of anyone else with the same condition (except a fictional
>character in George MacDonald Frazier's "Flashman" novels, which hardly
>counts.)
>
>So: what is the name of this condition? Is it genetic or something in
>the prenatal environment? Is is related to the more common condition
>where a person (or a cat or dog) can have each eye a single different
>color? Etc. I'm interested in any information anyone has.

The general morphological description is called "heterochromia
irides", which
means nothing more in plain English than "differently colored irises."

In that, the condition is not normal, and even though the bearer may be
completely non-impeded by its presence, it is a genetic "defect."
However, it
is often more serious than that. Heterochromia irides, especially when it
refers to eyes of two different colors -- but sometimes in eyes where one iris
is either splotchy with both blue and green/brown colors or evenly divided into
two differently colored hemispheres -- is a primary diagnostic character for
Waardenburg Syndrome (see:
http://www.icondata.com/health/pedbase/files/WAARDENB.HTM ), a developmental
abnormality that is common to many large mammals, exactly as you suggest.

Humans, cats and dogs that exhibit eye colors that are quite markedly
differently colored, where one eye is blue and the other green or brown, are
often mildly to profoundly deaf. The abnormality appears to be due to a point
defect in the pax-3 gene, a homeo box gene that is widely expressed during
early embryogenesis, thus explaining the wide range of effects that the gene
has.

Waardenburg Syndrome is inherited dominantly, however it is suspected that only
perhaps 20% of those bearing some form of the defect are actually aware of it,
its effects being so mild in most people.

More information can be found at:

    http://www.boystown.org/deafgene.reg/waardsx.htm

Wirt Atmar

======================================

Wirt Atmar
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