A targeting vector was designed to insert an IRES-Cre cassette followed by an FRT-flanked PGK-Neo cassette into the 3' region of the wingless-related MMTV integration site 3A (Wnt3a) locus. This construct was electroporated into C57BL/6-derived Bruce4 embryonic stem (ES) cells. Chimeric mice were bred to albino B6(Cg)-Tyrc-2J/J mice. The resulting Wnt3a-IRES-Cre mutant mice were then bred to C57BL/6J inbred mice for many generations. At some point, Wnt3a-IRES-Cre mutant mice were bred with FLPe-expressing mice on a C57BL/6 congenic background thereby removing the FLPe-expressing transgene.