Pigmentation is the coloring of a living organism. Pigmentation is produced by cells called melanocytes in the skin. Melanin is the pigment that gives color to human skin, hair, and eyes. The production of melanin is controlled by genes. Mutations in these genes can lead to changes in pigmentation.
Pigmentation serves several important functions in animals and plants. In mammals, it helps protect the skin from ultraviolet (UV) radiation from the sun. Darker-skinned people have more melanin and therefore better protection against UV radiation than lighter-skinned people. Pigmentation also plays a role in thermoregulation, as it helps absorb and reflect heat away from the body. In some animals, such as reptiles and fish, pigments help camouflage them from predators or prey.
There are two main types of pigmentation: eumelanin and pheomelanin. Eumelanin is brown or black and is found in the skin, hair, and eyes of humans and other mammals. Pheomelanin is red or yellow and is found in the feathers of birds and the scales of some fish and reptiles. Both types of pigments are made up of smaller units called chromatophores.
Eumelanin consists of two main types: brown eumelanin and black eumelanin . Brown eumelanins are mixtures of two compounds: dihydroxyindole (DHI) and dihydroxyindole-2-carboxylic acid (DHICA). Black eumelanins are made up of DHI and DHICA mixed with another compound called 5 ,6 -dihydroxyindole-2-carboxylic acid (DHICA). The ratio of DHI to DHICA determines the darkness of the pigment . More DHI results in a darker pigment .
Pheomelanins are reddish because they contain sulfur atoms . There are three main types: cysteine – rich pheomelanins , glycine – rich pheomelanins , and mixed type pheomel anins . Cysteine – rich pheom ela nin s get their color f ro m thiol groups (- SH), while glycine -rich p heome lan ins get their c olor fro m amide groups (- CONH 2 ). Mixed type p heome lan ins contain both thiols a nd amides .