Fig. 1

B.alapaav and B.arapaav are left-right homologs and B.al/rapaav death is dependent on engulfment and suicide genes. a The B.alapaav and B.arapaav cell lineages. Figure adapted from Sulston et al. [16]. b B.alapaav and B.arapaav are located close to each other and to the engulfing cell P12.pa in the developing male tail. Cell nuclei were traced from a DIC image of an otherwise wild-type male of genotype nIs343[P _egl-1 ::4xNLS::gfp]; him-8 just before the fourth larval stage, about 34 hours after hatching. Scale bar: 10 μm. DIC Z-stack of this animal is available as Additional file 1: Movie 1. c A schematic of the movements of B.alapaav and B.arapaav (blue) as viewed from above the animal. At the time of their generation, B.alapaav and B.arapaav are located to the left and right sides of the rectum. They move closer to the midline, ventral to the rectum. Eventually, the B.al/rapaav homolog will move closer to the midline, and B.al/rapaav typically moves slightly posterior and further from the midline. The B.al/rapaav homolog survives, and B.al/rapaav will undergo programmed cell death. In this diagram, B.alapaav is the dying B.al/rapaav and B.arapaav is the surviving B.al/rapaav homolog. d The percentages of late fourth larval stage males with a living P _egl-1 ::4xNLS::gfp-expressing secondary B.al/rapaav (i.e. B.al/rapaav was neither absent nor fully-refractile by DIC, see main text). All genotypes include nIs343 and some also contain †: him-5(e1490), ‡: him-8, °: nIs349, §: lon-1(e1820) dpy-17, : lon-1(e185), ★: unc-32. n.s.: P > 0.5, *: P < 0.005, **: P < 10⁻⁵