A loxP-flanked neomycin resistance cassette has been inserted into the fourth of five HpaII sites within the LRRFIP1/GCF2 (leucine-rich repeat in FLII-interacting protein 1/GC-binding factor 2) repressor protein consensus binding sequence in the first differentially methylated region (DMR1) upstream of the imprinted insulin-like growth factor 2 (Igf2) gene.