Silkie the "SHH" gene, called the ZPA Regulatory Sequence (ZRS). This causes ectopic "SHH" expression in the anterior of the developing limb bud, leading to increased tissue growth and digits. While the feet of the Silkie display polydactyly, the wings have the standard tridactyly (three digit) arrangement. The Japanese Silkie initially develops additional digits in the wing as an embryo, but these are lost prior to hatching. The genetic cause behind Silkie polydactyly differs from those that cause polydactyly in the Dorking chicken breed, which is due to ectopic "FGF4" expression in the AER, with ectopic "SHH" a secondary effect. The
Silkie covers the earlobes. They also are separated according to color. Colors of Silkie recognized for competitive showing include black, blue, buff, grey, partridge, and white. Alternative hues, such as cuckoo, lavender, red, and splash also exist. The standards of perfection call for all Silkies to have a small walnut-shaped comb, dark wattles, and turquoise-blue earlobes. In addition to these defining characteristics, Silkies have five toes on each foot. Other breeds which exhibit this rare trait include the Dorking, Faverolles, and Sultan. All Silkies have black or bluish skin, bones and grayish-black meat; their Chinese language name is "wu gu ji"