Fig. 8. Quantitative comparisons of features of morphogenesis of the wild-type notochord domain (blue) and the ntl mutant axial domain (red) during gastrulation and early segmentation stages. Values in A-C are normalized to 1.0 at the first time point. (A) Convergence: the domain widths are computed from values of k_C, estimated as in Fig. 3 at each time point (see Materials and Methods). Convergence is markedly decreased in the mutant until about 9.5 hpf. (B) Extension, domain lengths are computed from values of k_E, estimated as in Fig. 3 at each time point. In ntl mutants the axial domain extends rapidly during the same interval when the convergence is occurring slowly or not at all. (C) Area=widthxlength. The area is not expected to change if MIB alone underlies convergence and extension. Area only slightly decreases in the wild type, but increases in the mutant. (D) Cellular densities (number of cells per unit area). The density in wild type remains approximately constant during gastrulation and then increases. In the mutant, the density decreases, as would be expected if the field is increasing in area, extending but not converging.

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