Fig. 1. vab-1/Eph is synthetic lethal with sax-3/Robo and displays gene-dose sensitivity. The percentage embryonic lethality of single mutants and double mutant combinations between vab-1, sax-3 and slt-1 is shown. All alleles of vab-1 tested are 100% embryonic lethal with the sax-3(ky123) null. The null allele of vab-1(dx31) displays a dosage sensitivity with sax-3 in that embryos are dead even in the presence of one wild-type copy of vab-1. +/dx31; 0/sax-3 males are also dead. The double heterozygous embryos +/dx31; + or 0/sax-3 includes hermaphrodites and males, and the lethality is greater than 50% (57%), suggesting some non-allelic, non-complementation. By contrast, control crosses + or 0/sax-3 gave 27% embryonic lethality. vab-1; slt-1 does not display synthetic lethality but the phenotypes are enhanced. Error bars represent s.e.m. of at least three broods; n, total number of embryos scored for each genotype.