Fig. 2. Spindle orientations during cleavage of ABa and ABp in wild-type and it143 mutant embryos. All embryos are viewed ventrally just prior to and during second AB cleavage (see Materials and methods). Double-headed arrows indicate orientations of the ABa and ABp spindles. (A-C) Normal spindle orientations in a wild-type embryo. (D-L) The aberrant spindle orientations in three abnormal it143 mutant embryos at 20°C. The embryo in G-I developed into a sinistral adult, while the other two mutant embryos (D-F and J-L) were inviable.