Requirement for IrxB genes in pectoral fin development. (A) Alcian Blue (cartilage) and Alizarin Red (bone) staining of pectoral fins shows reductions of the scapulocoracoid cartilage in IrxBa−/−; IrxBb+/− mutants. (B) Summary of genotypes for the reduced pectoral girdle phenotype from a quintuple heterozygous in-cross. P-values report chi-square tests for deviation from the expected 1:2:1 wild type:heterozygous:homozygous Mendelian ratio. (C) Model highlighting the conserved roles of IrxB genes in development of proximal structures of the mouse forelimb and zebrafish pectoral fin. Green shading indicates regions for which development is dependent on IrxB/IrxBa. Cl, cleithrum; ED, endoskeletal disc cartilage; Hu, humerus; POP, postcoracoid process; Ra, radius; S, scapula; Sc, scapulocoracoid cartilage; Ul, ulna. Scale bar: 100 µm.
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