Description:
Extended brown in button quail is almost identical to the EB gene in coturnix quail. It creates an almost all brown bird, with the typical orange feet and slight black markings on the back. It strips the remarkable "bib" found on the wildtype and dilutes, making it impossible to feather sex in homozygous form. It is also often called the Blue Faced gene, or Blue Face in buttons.
The EB gene increases the eumelanin pigment in the bird's body, the same pigment that makes human hair and eyes brown. It does the same for quail. Each feather will have slight black horizontal barring, giving the bird an even darker look. There is a wide range of natural color for any EB bird, from a bluish brown to a deep chocolate, but in almost all cases, the darker brown is preferred.
In homozygous form, the bird is all brown and black. In heterozygous (one copy), there will be some faint blue leakage in the back and breast feathers, and males may have some red coloration near the vent, but the majority of the bird will be a dark brown.
Breeding with EB:
Blue Faced x Blue Faced = 100% Blue Faced
Blue Faced x Wildtype = 100% Blue Leakage
Blue Faced x Blue Leakage = 50% Blue Faced, 50% Blue Leakage
Blue Leakage x Blue Leakage = 25% Blue Faced, 50% Blue Leakage, 25% Wildtype
Blue Leakage x Wildtype = 50% Blue Leakage, 50% Wildtype
References & Further Reading
Kageyama, M., Takenouchi, A., Kinoshita, K., Nakamura, Y., & Tsudzuki, M. (2018). The “extended brown” plumage color mutant of blue-breasted quail (Coturnix chinensis) is associated with a mutation in the Melanocortin 1-Receptor gene (MC1R). The Journal of Poultry Science, 55(4), 233-238.
Araguas, R. M., et al. "MC1R polymorphism associated with plumage color variations in Coturnix chinensis." Animal genetics 49.5 (2018): 475-477.