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Color vision deficiency is one of the most common genetic disorders in the United States. Color vision deficiency is the inability to distinguish certain shades of color or in more severe cases, see colors at all. The term "color blindness" is also used to describe this visual condition, but very few people are completely color blind. (http://www.aoa.org) CVD is a genetic disorder in families that is passed down from parents to their children. (Evans, 2003 color is in the eye of the beholder pgs 4-5) people with dichromatic vision require only two colors of light, either red or green. Some 10 million American men—fully 7 percent of the male population—either cannot distinguish red from green, or see red and green differently from most people. This is the commonest form of color blindness, but it affects only .4 percent of women. The fact that color blindness is so much more prevalent among men implies that, like hemophilia, it is carried on the X chromosome, of which men have only one copy. (As in hemophilia, women are protected because they have two X chromosomes; a normal gene on one chromosome can often makes up for a defective gene on the other.) http://www.hhmi.org/senses.
The color receptors (cones) in the eyes of people with protanopia are not sensitive to long wavelengths (the reds). Reds look more like beiges and appear to be somewhat darker than they actually are. The greens tend to look similar to the reds. Protanomaly is milder than protanopia, but the end result is similar. Although many people with protanomaly can distinguish some reds and greens, they cannot do so as easily as someone with color-normal vision, and, as with protanopia, reds tend to look darker as well. Deuteranopia and deuteranomaly are the most common forms of color-blindness. People with these conditions have cones that are insensitive to medium wavelengths (greens), but the end result is similar to protanopia, with...