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Genetics of skin color in chickens

The phenotypic diversity of skin color in wild and domestic animals is an important characteristic for biologists and breeders. The color of the skin can be a sign of the breed. Some people prefer a bird with a dark skin color; such meat is considered more delicious and nutritious. In European countries, yellow-skinned or white-skinned birds are preferred.The variety of skin colors depends on a combination of specific genes that affect the deposition of xanthophylls and melanins, polygenic modifiers, and environmental factors. The yellow color of the egg yolk, as well as the white or yellow color of the skin and fat, is caused by carotenoids and xanthophylls. The dark colors of the skin and feathers depend on melanin, which is divided into eumelanin - the black pigment of the eyes, plumage, connective tissue and skin, and pheomelanin, which determines the brown shades of the plumage.Even in the last century, the Mendelian inheritance of white and yellow skin color in chickens was studied and the autosomal genes (W, w) that cause it were determined. Later in 2008, associations of the W locus with the beta-carotene dioxygenase 2 (BCDO2) gene were found. The results of these studies also changed earlier ideas about the origin of domestic chicken.Studies of the genetics of dark skin color were conducted on hyperpigmented silk breed of chickens. Classical breeding experiments have determined that this trait is controlled by two interacting genes: a sex-linked cutaneous melanin inhibitor (Id) and autosomal fibromelanosis (Fm).In 2010, the Fm gene that causes skin tissue hyperpigmentation was associated with the endothelin 3 (EDN3) gene. Beta-1,4-Galactosyltransferase, polypeptide 1 (B4GALT1), and versikan (VCAN) genes have been proposed as candidate genes for Id. Later in 2017, the GRAM domain gene containing 3 (GRAND 3) was proposed as the most likely candidate gene for the Id locus. However, no mutations significantly associated with this trait were found in GRAND 3.As a result of a century-long history of studying the genes that determine skin color in chickens, exact associations with the sex-linked skin melanin inhibitor Id have not been determined. Thus, this problem requires further study.