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
Blue Bird Mini Bird P30 step-van chassis and was initially available only with a gasoline engine. In the 1980s, diesel engines (the Chevrolet 6.2L) became an option. In the 1990s, the 6.2L diesel V8 was replaced with a more powerful 6.5L diesel. Unlike other models in the Blue Bird lineup, the Mini Bird was not assembled in Fort Valley, Georgia. Assembly of the Mini Bird took place in Buena Vista, Virginia (Blue Bird East; which closed in 1992) and in Mount Pleasant, Iowa (Blue Bird Midwest, which closed in 2002). Blue Bird Mini Bird The Blue Bird Mini Bird was a Type B school