Stag1^{Gt(P099A04)Wrst}

A rFlpROSA-geo cassette containing a splicing acceptor site and a polyadenylation sequence inserted between exons 3 and 4 of the gene. The insertion creates a null allele with no detectable transcript or protein expressed from this allele, and embryos carrying this allele turn blue upon incubation in X-gal.