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 oz) (12in)and for the female, 907 g (32 oz)(10in). The "Australian Poultry Standard" and "British Poultry Standard" call for Silkie bantams much smaller; in the Australian, the standard weights are 680 g (25 oz) for males and 570 g (20 oz) for females. The British standard weight for bantam Silkies is 600 g (22 oz) for males, and 500 g for females (18 oz). Silkies are also known for their polydactyly, usually manifesting as an additional 1-2 digits in the foot. The genetic cause of this extra digit formation has been shown to be a SNP in a regulator of