Blood glucose levels of mice from five strains were measured. The results showed that each strain was different from the others for genes affecting blood glucose level, although the strain differences were small.
Within strains, the chief sources of variation were sex differences, differences between mice from different litters of the same mother, and between mice assayed in different months. Repeatability of measurements on individual mice was low. Genetic analysis, even by biometrical techniques, was not possible because the small genetic effects were obscured by variation due to other causes.