a Upper graph: Brood size of endu-2(tm4977), after 4× initial backcrosses with wild type (G0), decreases over generations at 20 °C. Lower graph: The reproduction defect of endu-2(tm4977) animals is reversible by shifting the animals to 15 °C. To obtain this graph, adult animals from G6 that had been maintained at 25 °C were shifted back to 15 °C and counted as G0. As the numbers of generation to reach 100% sterility at 20 °C varied from 10 to 20 among the four biological replicates, only one represented replicate with n = 15 animals for each generation is shown. The data are mean ± SEM. b The sterile endu-2(tm4977) animals display multiple defects in germline mitosis and meiosis. (I–IV) DIC images of wild type and sterile endu-2(tm4977) animals 24 h after mid-L4 stage. The white arrows point to (II) increased number of germline apoptotic corpses; (III) empty gonad due to germ cell death; (IV) prolonged spermatogenesis; (V) DAPI staining of germline proliferating zone of day-one wild type and (VI) sterile endu-2(tm4977) adults, respectively. White arrows in VI point to abnormally large chromosomes due to endomitosis. Scale bar 10 µm. N = 3 biological replicates.