This allele was created in ES cells carrying the Six4tm1Kwk mutation in which the region of exon 1 encoding the Six homologous region and homeobox was replaced with an in-frame lacZ-neo cassette. The targeting event resulted in the entire sine oculis-related homeobox 1 homolog being replaced with an EGFP and a hygromicn-B-phosphotransferase gene. (J:114468)