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
What a queer bird in Chicago", with the work allegedly first printed in the "Bulletin of the Chicago Board of Education". The "Chicago Ledger" printed the work its "Jokes and More Jokes" section in May 1922, where the word "wonderful" replaced "queer". In July 1922, it appeared as a verse of imprecise origin in the "American Consular Bulletin". When printed in the "Pleasantries" section of "The Christian Register" in September 1922, it was attributed as a "[c]omposition by foreigner in a Chicago night school." By 1980, it was published as a folk song to be sung as a round. What a queer bird "What