The Mystery of Tetrachromacy • Hacker News Board

Re: The Mystery of Tetrachromacy

#11

Post by OopsCriticality » Sun, Dec 20, 2015, 5:53 PM UTC

peter303 wrote: post #7

Scientists are looking at direct delivery of gene therapy to retinal cells to cure serious eye diseases like macular degeneration, pigmentosa blindness, etc. Should this work well, then the next step would be lesser conditions like male color blindness. I read of some successful attempts to give dicromatic animals, genrally carnovoires, the trichromatic gene directly to the retina. These subjects can be tested by giv…

> The next step, more controversial, would be super-vision of tetrachromacity, perhaps infra-red and ultra-violet sensitivity. Night vision glasses no longer needed for enhanced soldiers.

Utter poppycock.

The cornea and lens in humans are UV opaque, which is a very good thing because UV light is damaging. People without a lens (aphakia) are reported to perceive UV light, but this is otherwise an undesirable condition. As to infrared, some people can already see up to around 750nm or so (NIR) with awful quantum efficiency. Pit vipers and some fish have limited perception of IR, but I'm not aware of any animals that can see IR in the conventional sense… being warm blooded presents a real problem, for one.

Plainly, there are limits to what can be achieved in hyperspectral imaging due to materials, and that's without the constraints of biology thrown in the mix.

Re: The Mystery of Tetrachromacy

#12

Post by xerula » Sun, Dec 20, 2015, 6:13 PM UTC

dspeyer wrote: post #6

First thought: The usual pattern is that only one X chromosome gets transcribed in any given cell.[1] This keeps the dosage of all those proteins correct. Otherwise there would need to be a separate set of dosage controls for XX and XY people. The inactivation occurs pretty early in life, and when cells replicate they keep the inactivation. This results in macroscopic regions of the body with consistent inactivation.…

The article explains X-inactivation, and it doesn't play the role you think here: both copies are broadly equally expressed among retinal cells. Also even if all cells in a retina used the same X-chromosome copy it doesn't predict color-blindness, since we would still have a trichromatic system.

The answer to the question posed by the title is simply that all mutant fourth cone types are not created equal. Most have a spectral response curve similar enough to an existing type not to make a real difference; a few have peak responses more squarely in-between those of the usual trichromat photopigments, allowing more finely graded color perception. (The article takes its time getting round to explaining this, but it's all there.)

Re: The Mystery of Tetrachromacy

#13

Post by guard-of-terra » Sun, Dec 20, 2015, 6:17 PM UTC

peter303 wrote: post #7

Scientists are looking at direct delivery of gene therapy to retinal cells to cure serious eye diseases like macular degeneration, pigmentosa blindness, etc. Should this work well, then the next step would be lesser conditions like male color blindness. I read of some successful attempts to give dicromatic animals, genrally carnovoires, the trichromatic gene directly to the retina. These subjects can be tested by giv…

I don't think we can get good infra-red vision.

Creatures with infra-red vision are usually cold blooded. We shine too brightly in infrared from within to be able to see something outside.

But tetrachromacy should rightfully belong to us. It was lost by our pre-mammal ancestors, while reptiles still have base tetrachromacy, and some fish perceive even more colors.

Most animals only perceive two colors and grow two pigments. Makes animal coloring (and animal world) kind of boring for us. Birds use bright colors because they can distinguish them.

Re: The Mystery of Tetrachromacy

#14

Post by Swizec » Sun, Dec 20, 2015, 7:10 PM UTC

bendykstra wrote: post #3

I learned the importance of trichromacy when a friend and I came across a patch of wild strawberries. I'm partially red-green colorblind and for every strawberry I found, my friend found ten. They were almost invisible to me. It's neat to see that the fourth cone's response curve peaks right between the red and green cones' curves in tetrachromats. I bet they are amazing at finding berries.

This probably has nothing to do with chromacy, but is related to finding berries and other odd things. My sister is gifted with finding four leaf clovers. She walks in a field and seems to just see them. Every time she picks one, it's a four leaf. Her record find is a 7 leaf clover.

I always wondered how that's possible.

Re: The Mystery of Tetrachromacy

#15

Post by colechristensen » Sun, Dec 20, 2015, 7:24 PM UTC

peter303 wrote: post #7

Scientists are looking at direct delivery of gene therapy to retinal cells to cure serious eye diseases like macular degeneration, pigmentosa blindness, etc. Should this work well, then the next step would be lesser conditions like male color blindness. I read of some successful attempts to give dicromatic animals, genrally carnovoires, the trichromatic gene directly to the retina. These subjects can be tested by giv…

I just visited my retina guy and he told me about the latest developments. These days they're modifying the genome of stem cells and printing small clusters of retinal cells onto a substrate for implantation.

There have been some successes curing serious blindness issues but they will be hesitant for a good long while to "cure" things like colorblindness. If things go wrong a blind person is still blind, but a colorblind person has quite a bit to lose.

Re: The Mystery of Tetrachromacy

#16

Post by such_a_casual » Sun, Dec 20, 2015, 7:35 PM UTC

bendykstra wrote: post #3

I learned the importance of trichromacy when a friend and I came across a patch of wild strawberries. I'm partially red-green colorblind and for every strawberry I found, my friend found ten. They were almost invisible to me. It's neat to see that the fourth cone's response curve peaks right between the red and green cones' curves in tetrachromats. I bet they are amazing at finding berries.

What does it mean to be partially red-green colobrlind? Isn't it the case that you either have the red-green cone or you don't?

Re: The Mystery of Tetrachromacy

#17

Post by nitrogen » Sun, Dec 20, 2015, 7:52 PM UTC

such_a_casual wrote: post #16

bendykstra wrote: post #3

I learned the importance of trichromacy when a friend and I came across a patch of wild strawberries. I'm partially red-green colorblind and for every strawberry I found, my friend found ten. They were almost invisible to me. It's neat to see that the fourth cone's response curve peaks right between the red and green cones' curves in tetrachromats. I bet they are amazing at finding berries.

What does it mean to be partially red-green colobrlind? Isn't it the case that you either have the red-green cone or you don't?

It's conceivable that a mutation in the gene for the red or green light-sensing protein gets a mutation that just shifts its sensitive wavelength closer to the other. So "partial" r/g colorblindness could occur if there was still some separation between those wavelengths, but not as much as is typical.

Re: The Mystery of Tetrachromacy

#18

Post by qb45 » Sun, Dec 20, 2015, 8:34 PM UTC

I wonder how those poor women deal with RGB displays. It must feel weird to see a difference between red+green and actual yellow.

Although, on second thought, color vision doesn't seem to work perfectly anyway. I never understood how red+blue can be perceived the same as far violet, it just doesn't make sense if you look at those frequency response curves.

Re: The Mystery of Tetrachromacy

#19

Post by metasean » Sun, Dec 20, 2015, 8:42 PM UTC

Swizec wrote: post #14

bendykstra wrote: post #3

I learned the importance of trichromacy when a friend and I came across a patch of wild strawberries. I'm partially red-green colorblind and for every strawberry I found, my friend found ten. They were almost invisible to me. It's neat to see that the fourth cone's response curve peaks right between the red and green cones' curves in tetrachromats. I bet they are amazing at finding berries.

This probably has nothing to do with chromacy, but is related to finding berries and other odd things. My sister is gifted with finding four leaf clovers. She walks in a field and seems to just see them. Every time she picks one, it's a four leaf. Her record find is a 7 leaf clover. I always wondered how that's possible.

Is it possible she has synesthesia (https://en.wikipedia.org/wiki/Synesthesia)?

Re: The Mystery of Tetrachromacy

#20

Post by deckar01 » Sun, Dec 20, 2015, 9:05 PM UTC

such_a_casual wrote: post #16

bendykstra wrote: post #3

I learned the importance of trichromacy when a friend and I came across a patch of wild strawberries. I'm partially red-green colorblind and for every strawberry I found, my friend found ten. They were almost invisible to me. It's neat to see that the fourth cone's response curve peaks right between the red and green cones' curves in tetrachromats. I bet they are amazing at finding berries.

What does it mean to be partially red-green colobrlind? Isn't it the case that you either have the red-green cone or you don't?

> Deuteranomaly ... The medium-wavelength pigment is shifted towards the red end of the spectrum resulting in a reduction in sensitivity to the green area of the spectrum. [0]

The closer the spectrum perceived by the M (green) cone is to L (red) cone, the harder is is to differentiate red from green.

[0] https://en.wikipedia.org/wiki/Color_blindness#cite_ref-KallC...