Genetic effects on coat colour in cattle: dilution of eumelanin and phaeomelanin
pigments in an F2-Backcross Charolais x Holstein population.
In this work, we follow the proposal of Van Grouw (2006), who considers leucism as a partial or total lack of eumelanin and phaeomelanin
due to an inherited disorder in pigment transfer, which causes fail in melanin deposition within cells, although maintaining pigments in the back of the eyeball but not in the iris.
Proposed mechanisms of its action include inactivation of the melanogenic enzyme, tyrosinase, influencing the switch from eumelanin to phaeomelanin
. [66,67] During melanogenesis, tyrosinase is responsible for the conversion of L-tyrosine to L-DOPA and subsequently to dopaquinone, then the pathway bifurcates to produce eumelanin or phaeomelanin
Hair has two types of pigments: eumelanin (dark brown or black pigment) and phaeomelanin
(light, reddish-yellow pigment).
Albinism is defined as a total lack of both melanins (eumelanin and phaeomelanin
) in feathers, eyes, and skin as a result of an inherited absence of tyrosinase.
Schizochroism, meaning "split colors", is a mutation resulting from absence of a melanin pigment (for example Van Tyne and Berger 1976), but would only be possible if Hairy Woodpeckers possess both types of melanin pigments (eumelanin and phaeomelanin
); whether or not they do was not revealed in our search of the literature.
The [C.sup.ch] mutation stifles production of phaeomelanin
, which is responsible for darker background coloration.
There are two chemical forms of pigment in human hairs: eumelanin and phaeomelanin
. The pigment eumelanin manifests in the colors of brown and black, and phaeomelanin
in the colors of yellow and red, with each pigment having a slightly different size and shape.