Fig. 8. Tbx1 heterozygous conditional phenotype. (A) Tbx1^+/- mice have aplasia of the left fourth pharyngeal arch artery (PAA), as shown by sagittal histological sections at E10.5 (arrow indicates third PAA). (B) Conditional heterozygous mice appear normal at the same stage, with both the third and fourth PAA clearly present (arrows). (C,D) E17.5 Tbx1^+/- embryos have RSA (arrow in C), whereas all conditional heterozygotes appear normal (D). The right subclavian artery in the conditional mutant (D) is indicated with an arrow. +/-, Tbx1^+/-; PEKO/+, Tbx1 flox/+; Foxg1-Cre/+. Scale bars: 200 µm in B,D.