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In segregating F(2), F(3), and F(4) generations, albino mice had lower activity and higher defecation scores than pigmented animals when tested in a brightly lighted open field. These differences persisted when members of an F(5) generation were tested under white light, but largely disappeared under red light. Thus it was concluded that there is a major gene effect on the quantitative traits of open-field activity and defecation which is mediated by the visual system and that albino mice are more photophobic than pigmented mice under conditions of bright illumination.

Ovaries from donors of each of two inbred strains (BALB/cJ and C57BL/6J) were transplanted into F1 hybrid recipients. By appropriate matings it was thus possible to obtain inbred offspring carried by either hybrid or inbred mothers. Differences in the maternal environment were found to account for a relatively small proportion of the total variance in open-field behavior, but accounted for a relatively large proportion of the variance in body weight.