Accelerated breeding analysis of Fyn-null mice. Fifteen Fyn-null and seven wild-type (WT) breeding pairs, at least 6 weeks of age, were set up and maintained for 10 months using an accelerated breeding program wherein mice were bred on the post-parturient oestrus. Pup delivery was checked daily to record the delivery date, numbers and sex. Pups were removed upon weaning at 18–19 days after birth to allow subsequent matings. Values on the vertical axis represent the mean ± s.d. litter size from the different female mice, whereas the x-axis lists the number of pregnancies. (a) Fyn-null female mice produced significantly smaller litters (marked with a single asterisk): 1st, P < 0.022; 2nd, P < 0.043; 3rd, P < 0.028; 4th, P < 0.001; 5th, P < 0.001. (b) The interval of pup delivery was significantly extended in Fyn-null female mice compared with WT mice (marked with a double asterisk; P < 0.025).