Living offspring were obtained from all 37 strains with either the conventional (black) or the improved (gray) embryo transfer method. While 10 out of 35 strains failed to produce offspring by the conventional method, all strains tested produced offspring successfully by the improved method (33 strains). Offspring of the SWN strain were born in combination of embryos derived from natural mating and the improved embryo transfer method (asterisk). The detailed data set is available in Table S6. N.T., not tested.