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
The Great Silkie of Sule Skerry selkie is rather a "grey" selkie. The ballad begins: A synopsis is as follows: A woman, nursing a baby, laments that she does not know the child's father or where he lives. A man rises up to tell her that he is the father, and that he is a silkie — a changeling that takes the form of a man on the land and a seal in the sea, and that he lives on a remote rocky island called Sule Skerry. He gives her a purse full of gold, takes his son, and predicts that she will marry a gunner