Fig. 9

A phenotypic series of anterior arch mutants, arranged in approximate order of severity (unpublished examples, C.T.M; see also Kimmel et al., 1998). (A) Alcian-stained flat mounts of mandibular and hyoid cartilages. Abbreviations and orientation are as in Fig. 1D. The three mutations are at three separate loci; sucker (suc) encodes Endothelin-1; sturgeon (stu) and schmerle (she) have not been identified molecularly. The mutants are arranged by severity of the phenotypes, as judged by the amount of cartilage present in the mutants; stu^- is the least severe and suc^- the most severe. (B) Drawings illustrating our interpretation of the mutant phenotypes: Red, dorsal cartilages in the two segments; green, ventral cartilages; blue, the DV joint region, missing in mutants. We propose there is a change in polarity of the ventral cartilages in the mutants (see text). By this hypothesis, in WT the dorsal and ventral cartilages have opposite polarities. The polarities of the ventral cartilages (green arrows), which we suppose indicates their direction of outgrowth from the precartilage condensations, become progressively more like that of the dorsal elements (red arrows) with increasing severity of the phenotypes.