The neurological development of the nematode Caenorhabditis elegans is being analysed by classical genetic and molecular approaches. Putative transposon insertions have been generated using a mutator strain. The mutations isolated include an allele of the axonal growth gene
unc-44 and a mutation in a novel dumpy gene. These alleles are unstable, but the reversion rates and the number of extraneous transposons can be decreased by serial backcrosses to a transposon Tc1 low copy number strain. Hybridization of Tc1 DNA to gel blots of mutant DNA revealed a limited number of transposable elements in addition to the wildtype complement. In the case of the dumpy mutation, the association of a unique Tc1 element with the mutation has been demonstrated by loss of the