Re: Anyone here colorblind?

"Lisa Ann" <lisa-ann@[EMAIL PROTECTED]
> wrote:

>"Opus the Penguin" <opusthepenguin+usenet@[EMAIL PROTECTED]
> wrote in message 
>news:Xns9A9794F0CDF87opusthepenguinnettax@[EMAIL PROTECTED]
>> Which of our regular AFCAns is colorblind? We ought to have a few in a
>> group this size. Can you tell the difference between the image on the
>> left and the image on the right at this link:
>>
>> <http://www.studiocook.com/stuff/colorblinded.jpg>
>
>Scott's colorblind, although I can't remember which colors he can't see.
>
>The weirdest thing about it is that he's very light sensitive.  He can
see 
>things clearly in very dim light, whereas I have to start turning on
lights. 
>Until we figured out that it had to do with his colorblindness, we used
to 
>argue on when the "right time" to turn the lights on was - he insisted I 
>should be able to see (because he could) and I insisted that when I'm 
>banging into stuff because I can't see in the dim light, it's time to
turn 
>the freaking lights on.

There are two types of vision receptor, and one of those types is
divided into three subtypes.

Evolution has to balance the need for very sensetive night vision
"rod" receptors versus the need for colour-sensing "cone" receptors.
There are three kinds of cone sensors which give us our three primary
colours.  The gene coding for the red sensor is fairly new in
evolutionary terms, and so only exists in one place, and in a BAD
place on the X chromosome.  Men have no spare copy of this gene, so,
if the only copy goes bad, you don't get red.

I don't know what happens if you don't make red-detecting cones.  That
space in the retina will be filled, but I don't know whether the
shortage is made up with more green and blue sensing cones, or whether
there would be more rods.  From what you describe, it sounds like the
shortage of red cones was made up with low-light B/W rod cells.

(Change is not always "bad".  The red-sensing cone that is so valuable
to fruit-eating primates is clearly a mutation of one of the several
genes coding for blue-sensing cones.  Break it and you get something
more useful than  the original.)
-- 
Tomorrow is today already.
Greg Goss, 1989-01-27