(A–C) OPT images of wild type (WT), Six1-het (HET), and Six1-null (NULL) mouse heads reveal that, in addition to deformed skull and jaws, Six1-null mice present with BOR-like features such as ear tags (arrow in C). (D) Expression pattern for Six1 as seen with whole-mount ISH in WT E10.5 mouse embryo. Mandibular arches (dashed yellow box) were manually dissected and processed for RNA-seq. Ventral view. (E) Venn diagram showing the number of genes detected in each genotype. (F) Quantitative expression of Six1 and reference gene Gapdh in mandibular arches from each genotype. n=3 per genotype. Data was normalized with expression values for Actb. **P<0.01, ****P<0.0001, ns: not significant.