Everything about Dichromacy totally explained
Dichromacy in humans is a moderately severe color vision defect in which one of the three basic color mechanisms is absent or not functioning. It is hereditary and sex-linked, predominantly affecting males. Dichromacy occurs when one of the cone pigments is missing and color is reduced to two dimensions.
Organisms with dichromacy are called dichromats. Dichromats can match any color they see with a mixture of no more than two pure
spectral lights. By comparison, a
trichromat requires three pure spectral lights to match all colors in their
visual spectrum.
There are various kinds of
color blindness. Protanopia is a severe form of red-green color-blindness, where there's impairment in perception of very long wavelengths, such as reds. To these sufferers, reds are perceived as beige and greens tend to look like reds. Protanomaly is a less severe version.
Deuteranopia consists of an impairment in perceiving medium wavelengths, such as greens. Deuteranomaly is a less severe form of deuteranopia. Those living with deuteranomaly can't see reds and greens like normal people, however they can still distinguish them in most cases. A more rare form of color blindness is tritanopia, where there exists an inability to perceive short wavelengths, such as blues. Sufferers have trouble distinguishing between yellow and blue and tend to mistake greens for blues and yellows for reds.
Dichromacy in mammals
It is currently believed that most
mammals are dichromats. The straightforward exceptions are
primates closely related to humans, which are usually trichromats, and sea mammals (both
pinnipeds and
cetaceans) which are
monochromats.
New World Monkeys are a partial exception: in most species, males are dichromats, and about 60% of females are trichromats, but the
owl monkeys are
monochromats, and both sexes of
howler monkeys are trichromats. Recent research (for example Arrese et al, 2005) suggests that trichromacy may be widespread among
marsupials.
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