(A) Targeting construct, structures of the wild type and targeted Wnt8b alleles and probes used in Southern blotting to detect correctly-targeted clones. ‘End’ indicates the 5′ end of the 5′ homology arm and corresponds to the end of the λ clone from which the targeting vector was derived. H, HindIII; R, EcoRI; X, XbaI; N, NotI. (B,C) Southern blots using 5′ and 3′ flanking probes, showing correctly targeted ES cell clones. The 5′ probe detects an 11.3kb HindIII fragment in wild type DNA and a 10.3Kb fragment in the targeted locus. The 3′ probe detects an 11.3kb EcoRI fragment in wild type DNA and a 9.5kb fragment in the targeted allele. (D) Genotyping of mice carrying targeted allele (E) RT-PCR showing absence of Wnt8b mRNA in mutant telencephalon. (F,G) Absence of Wnt8b expression in dorsomedial telencephalon of E12.5 mutant embryo as judged by in situ hybridisation.