In this example, we're going to talk about color blindness, and specifically we're going to say that red-green color blindness is the most common form of color blindness, affecting roughly 8% of men. Now, just step back for a second. 8% of men is a heck of a lot of folks, right? So, there are a lot of people out there not able to distinguish between greens, yellows, oranges, and reds. Maybe you're one of them. Alright? Let's keep going. We have mutations to the gene opn1mw, and you can just read that sort of as opsin 1 medium wavelength, are the most common cause of red-green color blindness. This gene codes for the MWS or medium wavelength sensitive opsin. If a person did not produce the MWS opsin, at what wavelength of light would they no longer be able to distinguish different colors? Use evidence from the image to support your answer.

Alright. To figure that out, we need to reorient ourselves to the image. So, on the x-axis, we're from 350 to 700. We have wavelengths in nanometers. We also have this color scale that aligns roughly what most people perceive color as to the wavelength that causes them to perceive it. And then, on the y-axis, we have from 0 to 100, relative absorbance. We have 4 curves on this graph: the s-cone, the rods, the m-cone, and the l-cone.

Alright. So, straight off the bat, we're talking about color vision, so I don't care about the rods. Remember, rods have nothing to do with color vision, so I'm actually just going to try and sort of white out this rod's curve. I don't care about it or what we're talking about. Alright. So, get rid of the rods, and then I just want to start thinking alright. So, for this typical type of red-green color blindness, it's caused because the person doesn't make the medium wavelength-sensitive cone or, I'm sorry, sensitive opsin. That means that their medium wavelength cone isn't going to be functioning. So, we can basically also just erase this m-cone.

Right. So, someone who has this sort of most typical form of red-green color blindness, they're basically operating just with 2 cones in their eyes. They're operating with the s-cone and the l-cone. The m-cone isn't doing anything for them because they don't produce that opsin.

Okay. Now, to understand how this works, we've got to think about how color vision works. So, remember, we said to be able to see in color, you need a signal from multiple cones at the same time. You need to measure that relative signal to be able to distinguish wavelength. If you only get a signal from a single cone, you can't distinguish between intensity and wavelength.

So now, we've got to look where on this graph is someone going to get a signal from more than 1 cone. Well, they're going to get a signal from more than 1 cone, roughly from about here up to about here. So, in that range of roughly, what's that? 400 up to about 540. Okay. So, it's this region here that they get more than one signal, and people with typical red-green color blindness will be able to see color in this range, those blues, cyans, up to greens, pretty similar, pretty much like anyone else can.

But once you go over here on this graph, once you head up above 540, well, in this range, they're only getting a signal from a single cone, only from that l-cone. And if you get a signal from only one cone, you can't tell the difference between wavelength and intensity. People with red and green color blindness, right, they might see yellows, wavelengths, oh, I don't know, 570 here, 560. Those might look kind of intense or brighter. Reds might look dimmer, but they can't tell the difference in terms of color between those two things.

So to answer our question here, at what wavelength would they stop being able to perceive color? Well, we said that's about wavelength 540 nanometers. And my evidence is that from wavelength 540 to 700 nanometers, we're going to say they get a signal. There's a signal from only the l-cone. They're only getting a signal from a single cone, and if you get a signal from a single cone, you can't distinguish wavelengths; you can't see color. So people who are red-green color blind, again, they have fairly typical sight or fairly typical color distinguishing from the blues into the greens, but then starting in the greens here into the yellows and the orange, they can see intensity, but they can't distinguish color.

Alright. Hopefully, using this graph helped to make that a little bit more clear for you. We're going to keep going with more practice problems after this. I hope to see you there.