Mice that are heterozygous for the targeted mutation are viable, fertile, normal in size and, with the exception of a kinked tail, do not display any gross physical or behavioral abnormalities. Homozygous null mice have an embryonic lethal phenotype, failing to develop past embryonic days 10.5 to 12.5 dpc. The gene targeting strategy introduced a stop codon in exon 3 to produce a shortened inactive gene product. No full-length wildtype gene product (protein) is detected by Southern blot analysis of homozygous embryos. By 9.5 dpc homozygous mutant embryos exhibit loss or disruption of posterior structures caudal to forelimb bud, including truncated trunk, kinked neural tube, lost or disrupted somites and lack of tailbud formation. The Jackson Laboratory 2024, used with permission.