Fig. 1. Detection of lacZ gene expression in mouse embryos. (A) Summary of the staining for ß-galactosidase activity in embryos with different genotypes. (B) Representative staining for ß-galactosidase activity in day 13.5 embryos. Neither Lsh^–/– nor Zac1 mutants show any overt morphological abnormalities (Geiman et al., 2001) (C.L.S. and S.V.K., unpublished). lacZ gene expression was widely distributed in Lsh^+/+ and Lsh^–/– embryos when the lacZ gene was inherited from the paternal side. No expression was observed when the lacZ gene was propagated from the maternal side.