Heterozygotes are WT and segregate WT, DpyUncs, and Unc-4 animals which arrest at the L4 stage. Rarely, a recombination will occur and unc-4 and pir-1 will become unlinked. Propagate the strain by picking single WT animals and checking for correct segregation of progeny. 6/2007: Daniel Chavez notes that tm1496 may also delete part of sec-5, which could be responsible for the developmental arrest of tm1496.