Trichromate
Trichromats (Greek: tri- "triple" and chroma "color") are living beings that have three different types of cones as color receptors in the retina .
Occur
Among the higher mammals , only the Old World monkeys are consistently trichromats. These also counts man . In some New World monkeys , around two-thirds of the females are trichromats, which provides a possible indication of the origin of trichromatism in primates .
Even with bag mammals are found sometimes three different types of cones. However, this is likely to be a primarily preserved trichromaty. The other mammals, on the other hand, are dichromates . Birds, fish, reptiles and amphibians, on the other hand, are usually tetrachromates , with trichromatism also occurring.
Arthropods such as insects , crustaceans and arachnids are predominantly trichromats; tetrachromasia occurs less often. In addition to the blue and green receptors, arthropods also have a UV receptor, while the arthropods lack a red-sensitive sensory cell in the trichromats.
Color vision
With trichromats there are three types of cones with different absorption maxima, the red-sensitive L-cones, green-sensitive M-cones and the blue-sensitive S-cones. The brain creates a color image from the measured values of the L, M and S cones .
The cones have a low sensitivity, so they only work in good lighting conditions. In twilight or in the dark, their functionality decreases significantly. The more sensitive rods then take over the perception of light in the retina. However, since there is only one type of rod and therefore cannot distinguish between different wavelengths, color vision decreases with decreasing brightness.
Origin in primates
The pigment for longer-wave light is coded on the X chromosome in all mammals. It was therefore assumed that trichromaty in Old World monkeys was caused by gene duplication and subsequent mutation of one of the genes.
However, in squirrel monkeys , for example, the gene for the long-wave receptor occurs in three alleles , the sensitivity of which lies between that of the human M and L cones. Since the coding is also on the X chromosome, all males are dichromates. About two thirds of the females are trichromats, because their two X chromosomes make it possible to have two different alleles. Since the pigments of the cones in New World and Old World monkeys are almost identical, it is now assumed that the mutation and splitting into at least two alleles took place first and that gene duplication only occurred in Old World monkeys after the continents had separated.
Other forms
According to the trichromats there are
- Tetrachromat (four colors)
- Dichromate (two colors)
- Monochrome (one color)
Remarks
- ↑ L stands for long, long wavelength. Absorption maximum in humans about 560 nm.
- ↑ M stands for medium, medium wavelength. Absorption maximum in humans about 530 nm.
- ↑ S stands for short, short wavelength. Absorption maximum in humans about 430 nm.
Individual evidence
- ↑ a b c Gerald H. Jacobs, Jeremy Nathans : Color Sense of the Primates . In: Spectrum of Science . No. 05 , 2010, ISSN 0170-2971 , p. 44-51 .
- ↑ Gerhard Neuweiler, Gerhard Heldmaier: Comparative animal physiology . tape 1 : Neuro- and Sensory Physiology . Springer, Berlin / Heidelberg 2003, ISBN 3-540-44283-9 , pp. 463-473 .
- ↑ Gerhard Neuweiler, Gerhard Heldmaier: Comparative animal physiology . tape 1 : Neuro- and Sensory Physiology . Springer, Berlin / Heidelberg 2003, ISBN 3-540-44283-9 , pp. 515-516 .