Fig. 5. kra and shot genetically interact with robo. (A-F) The CNS in stage 16-17 embryos stained with mAb 1D4 (anti-Fasciclin II). In kra²/+ (A) or shot³/+ (B) heterozygous embryos, the longitudinal axon tracts never cross the midline as in the wild-type (see Fig. 4D). (C) In robo²/+ heterozygous embryos, the longitudinal axon tracts rarely cross the midline (0.9%). (D,E) The robo²/+ phenotype is significantly enhanced when one copy of kra and shot is also removed in robo²/+; kra²/+ (D) or shot³,robo²/+ (E) transheterozygous embryos. (F) This phenotype is also further enhanced in shot³,robo²/+; kra²/+ embryos. Anterior is to the top. (G) Quantification of the midline crossing frequency per segments in each of the indicated genotypes (n=180, 130, 446, 392, 976 and 488 segments, respectively). Statistically significant differences are denoted by an asterisk (control, robo²/+; P<0.001). Scale bar: 10 µm.