On Wednesday 12 June 2002 16:02, Maarten van Beek wrote:
> > Van: Tim May
> > Onderwerp: Re: CHAT: Orange
> >
> > I believe there are supposed to be people with a fourth cone
> > type... I seem to recall the word used was "tetrachromat".  Very
> > rare, though. Supposed to have exceptionally precise colour sense
> > - I'd suspect Cristophe was one with his "Indigo isn't a type of
> > blue",
> Probably...
> > but IIRC  they're all supposed to be female.

The way I remember it is this: the genes for red-sensing cones are on
the X chromosome and come in (at least) two alleles. One can
conceivably have an X chromosome with one allele and a second X
chromosome with a different allele. (This would, of course, make you
female, unless you are one of those special individuals with a triple
sequence of sex chromosomes, and then you would have many more
problems than color vision...)

Now, the cells in the eye that make cones contain both X chromosomes,
but only one will get expressed per cell, and it is not necessarily
the same one for each cell, leading to a situation where you could
have two types of red cones in your eyes, leading, supposedly to
better color distinctions.

However, when I went to my reference books and to google to confirm
this, I couldn't find it anywhere. So...?

I did, however, find the interesting fact that red opsin genes and
green opsin genes are 97% identicl, and thus diverged only a short
(evolutionarily speaking) time ago. Blue opsin genes are on a
completely different chromosome and are only ~43% identical with the
red or green ones. Also, old world monkeys and apes have all three
opsin genes and are trichromatic, just like most humans. New world
monkeys only have two (the red and green opsin genes are alleles of
each other, so some have red and some have green), and spider monkeys
have dichromatic males and trichromatic females... fun!

This is of course relevant only to those who are making non-human
languages, cultures, and peoples.


Sylvia Sotomayor
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