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 Silkie tour was subsequently cancelled. Two further singles released in 1966 failed to make either the UK or the US charts, and in the autumn the original Silkie lineup subsequently split. Mike Ramsden and Sylvie Tatler had married in January 1966, and they subsequently continued to perform as a duo version of The Silkie for a further 35 years (sometimes with their children) and often appeared at their local pub, The Cott Inn at Dartington, Devon. Ramsden also guested as a vocalist on the album "Western Flier", alongside the 20-year-old keyboard player Mike Batt, recorded in 1969 by the proto-psychedelic folk