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 an ideal year. Their capacity for incubation, which has been selectively bred out of most fowl bred especially for egg production, is often exploited by poultry keepers by allowing Silkies to raise the offspring of other birds. In addition to being good mothers, Silkies are universally renowned for their calm, friendly temperament. They do well in confinement, and interact very well with children. This docility can cause Silkies to be bullied by more active or aggressive birds when kept in mixed flocks. In the "American Standard of Perfection", the standard male weight for the bantam Silkie is 1 kg (36