A targeting construct introduced loxP sites surrounding exon 4 of mouse Smchd1 gene and a neomycin cassette flanked by Frt sites by recombineering. The neomycin cassette was removed by crossing with the FLPe knockin mouse strain. Cre-mediated recombination of Smchd1tm1.1Maar removed exons 4. Western blot analysis onfirmed the absence of wild-type protein in homozygous embryos at E12.5. (J:255702)