This allele was generated using the same targeting vector used to generate Hoxdtm4Ddu, which contained a floxed neo cassette followed 303 bp downstream by a 261 bp deletion of region X. The floxed neo cassette was deleted in vitro via cre mediated recombination, leaving a single loxP site and the 261 bp deletion in the intergenic region between Hoxd11 and Hoxd12. (J:49264)