
Description:
Extended black is a base plumage in chickens. It is found on the E locus, and is almost completely dominant (1). It causes an increased amount of eumelanin, or black pigment, in chickens, and is similar to the Extended Brown gene in coturnix quail and several mammals (2). Without additional dilutions, extended black birds are typically black or very dark, with black shank coloration and beaks (7). Almost all extended black based birds will have black feet and legs, most black variety birds with yellow or other light colored shanks are not based on EB. (8)
Extended black is confirmed on the MC1R gene, which was originally mapped to chromosome 1 in chickens and also linked to the pea comb gene (3), but recent studies have linked the gene to chromosome 11 instead (2), with much more robust methods then the original linkage maps. In the order of dominance, Extended Black is the most dominant of all of the genes on the E locus.
Chicks on with extended black bases typically are a dark grey to black color, with minimal white patches, assuming there are not additional color dilutions on top. (7) It was originally believed that chickens with extended black would be entirely black, but studies have shown that wildtype feathering in heterozygous form is possible (1). Without any other melanizers, there will be some minimal red leakage through the hackle of females. Males will have bright red hackles and saddle feathers, and look remarkably similar to birds based on birchen, but without the lacing through the breast. (8)
The APA currently recognizes black in the following breeds: Ameraucana, American Game, Australorp, d'Anver, Booted, Cochin, Cornish, Crevecoeur, Cubalaya, Dutch, Hamburg, Japanese, Java, Jersey Giant, LaFleche, Langshan, Malay, Modern Game, Old English Game, Orpington, Plymouth Rock, Rosecomb, Shamo, Sumatra, and Wyandotte.
In general, White Faced Spanish, Blue Andalusian, Castellana, and Minorca are based on extended black. (2)
It is worth noting that is it possible to get black in these breeds without using the extended black base. It is also possible to get a variety of different colors, including white, mottled, lacing, and other varieties on the extended black base by using different genes that restrict eumelanin. (4)
Breeding with Extended Black:
Extended Black x Extended Black = 100% Extended Black
Extended Black x Duckwing = 100% het. Extended Black
Extended Black x het. Extended Black = 50% Extended Black, 50% het. Extended Black
Het. Extended Black x het. Extended Black = 25% Extended Black, 50% het. Extended Black, 25% Duckwing
Het. Extended Black x Duckwing = 50% het. Extended Black, 50% Duckwing
Extended Black x Wheaten = 100% het. Extended Black, hidden Wheaten
Extended Black x Birchen = 100% het. Extended Black, hidden Birchen
References & Further Reading
Kerje, Susanne, et al. "Melanocortin 1‐receptor (MC1R) mutations are associated with plumage colour in chicken." Animal genetics 34.4 (2003): 241-248.
Shoffner, R. N., J. S. Otis, and V. A. Garwood. "Association of dominant marker traits and metric traits in chickens." Poultry science 72.8 (1993): 1405-1410.
SMYTH Jr, J. ROBERT. "Research note: linkage relationship between the pea comb (P) and extended black (E) loci of the chicken." Poultry Science 71.1 (1992): 208-210.
Guo, X. L., et al. "Genetic variation of chicken MC1R gene in different plumage colour populations." British poultry science 51.6 (2010): 734-739.
Dávila, S. G., et al. "Association between polymorphism in the melanocortin 1 receptor gene and E locus plumage color phenotype." Poultry science 93.5 (2014): 1089-1096.
American Poultry Association. (2023). American Standard of Perfection (45th ed.).
Spiegel, J. (n.d.). The E locus in chickens. Tumblr. Retrieved July 27, 2024, from https://www.tumblr.com/birdgenetics/747951459994370048/the-e-locus-in-chickens?source=share
Dort, Sigrid van, and David Hancox. Genetics of Chicken Colours : The Basics. Avicultura/Delta Press, 2009.
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