Polysyndactyly, a new mutant gene in the mouse.

The gene for polysyndactyly (Ps) arose during a neutron irradiation experiment at the M.R.C. Radiobiological Unit at Harwell (Batchelor, Phillips & Searle, 1966), and was offered to the author in November 1964. The mice from Harwell were outcrossed to CB $? (the Fx of CBA/Gr &?xC57 BL/Gr $?). The stock was outcrossed again in late 1966 to improve fertility. Rigorous brother/sister mating has not been practised. Embryos from Ps/ + xPs/ + matings were fixed in Bouin's solution, sectioned at 7-5 or 10/* according to age and stained with H & E. In most cases only the limbs were sectioned (left fore and hind limbs transversely, right ones tangentially). These included groups of 2 PsjPs, 2 Psj + and 2 + / + embryos aged 15 and 14 days and six 13-day embryos which could not be classified by inspection. Twelve 12-day and five 11-day embryos were sectioned intact in the transverse plane. Six litters aged 14 days were vitally stained with 1/40,000 Nile blue sulphate in isotonic saline. Methylene blue preparations were made following Griineberg's (1953) protocol (Table 1). Alizarin red S clearance preparations were made by a modification of Dawson's (1926) technique (Table 2). The feet of 15 Ps\ + and 15 + / + littermates were preserved in 10 % formol saline for detailed examination.