The aim of this study was to develop a new strain of osteopetrotic mouse for investigating genetic characteristics of op gene at an early age. B6C3Fe-a/a-op/+mice (Jackson Lab.) were mated with A/WYSNJ mice to obtain sibling F1 mice. Randomly sampled F1 mice were mated to obtain F2 mice. There were fourteen op/op mice out of the obtained sixty-three F2 mice. Erupted incisors of all F1 mice and the frequency of the F2-op/op mice was 22%, and it was concluded that the op gene has an autosomal

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... ssive character and mono-gene. Histopathological studies revealed that the F2-op/op mice showed similar femur bone structures to those of B6C3Fe-a/a-op/op mice. It is expected that this new strain of osteopetrotic mouse will be useful for investigating histopathological and genetic studies of osteopetrosis.