Figure 3. Phenotypes of Chrd^+/+,Tbx1^G>T/G>T and Chrd^−/−,Tbx1^+/+ mutant embryos.

(A) Crossing scheme to generate recombinant animals. 129S6-Chrd^+/− females were mated with 129S6 wild-type studs and offspring were screened for recombination of markers. (B) Penetrance of five phenotypes associated with DGS from each different Tbx1 mutant class, displaying dosage-dependent rescue of craniofacial phenotypes. (C–H) Variable mandible defects in Chrd^−/− mutant at late gestation stages. (C, D) Mild mandible outgrowth defect in B6-Chrd^−/− mutant embryo (arrowhead). (E–H) Total absence of mandibular elements accompanying incomplete midline structure (arrowhead) is displayed in lateral (E, F) and ventral view (G, H) of 129S6-Chrd^−/− mutant embryo. (I–L) Developmental defects of Chrd null, Tbx1 hypomorphic, and compound mutations. (I) Organs that are defective in various classes of mutant embryos. (J) Chrd null mice display a truncated mandible phenotype at low penetrance. (K) Tbx1 hypomorphic embryos develop very mild craniofacial defects (note partially dysmorphic ear) compared to Tbx1 null embryos.