Single Gene Gives Mice Three-Color Vision

maynard writes "A study in the peer-reviewed journal Science shows that mice transgenetically altered with a single human gene are then able to see in full tri-color vision. Mice without this alteration are normally colorblind. The scientists speculate that mammalian brains even from animals that have never evolved color vision are flexible enough to interpret new color-sense information with just the simple addition of new photoreceptors. Such a result is also indicated by a dominant X chromosome mutation that allows for quad-color vision in some women." A sidebar in the article includes a nice illustration of what two-color vs. three-color mice might perceive.

Comments

Re:True colour

[blueish yellow]

Violet is especially tricky. Its wavelength is shorter than blue, but in addition to stimulating your blue cones, your red cones are also slightly sensitive to it.

This doesn't make any sense. Red cones are not sensitive to blue light. Here is a diagram showing the sensitivities of of the three cones (S, M, and L or Blue, Green and Red) in our retina whose signals combine to create color.

Our perception of color comes from the combination and comparison of the stimulation of three different cones, each maximally sensitive to different wavelengths. The output of the cones gets combined in what are called opponent pathways, one is Red-Green, and the other is Blue-yellow. The Red-Green pathway compares the output of the Red and Green cones and the Blue-yellow pathway compares the output of the blue cone with the sum of the red and green cones. This is why you will never see a color that is reddish-green or blueish-yellow (see nick) at least in the additive sense that red+blue=violet and yellow+blue+green.

So why does extremely short wavelength light appear to contain a reddish component? I don't believe that anyone knows the answer to that yet. But the hypothesis is that somewhere along the path from cone to cortex the input from a blue cone and red cone combine which turns our perception of an extremely short wavelength light into a combination of short wavelength light (blue) and extremely long wavelength light (red). So our sensation of color becomes a continuum that loops back on itself as opposed to our sense of pitch (which is also frequency or wavelength).

Interestingly people who have had their lenses removed are somewhat able to perceive ultraviolet light. This is because the lens ordinarily blocks UV light and blue cones are sensitive to UV light but very little ever penetrates to the retina normally. Apparently they see it as lilac.

Many mammals, fish, birds, insects, and reptiles (basically everyone except us) are able to see UV light as well. It's a good that we can't for two reason. One is that there is more chromatic aberration at shorter wavelengths. Basically blue light bends more than red light. This makes focusing more difficult. Also, more importantly, UV light damages DNA which is a very, very, bad thing. This is a good resource for learning more.

Re:Question I couldn't get from the article

[inviolet]

Also, gene theropy into retinal is very difficult because (thank god) there are very few viruses that infect retinal cells.

Don't thank god for that, thank natural selection. A virus that impairs its host's vision is not going to get much time to reproduce itself.