273 Mutation Research, 80 (1981) 273--279 © Elsevier/North-Holland Biomedical Press FORMALDEHYDE MUTAGENESIS IN THE NEMATODE Caenorhabditis elegans D.G. MOERMAN and D.L. BAILLIE Department of Biological Sciences, Simon Fraser University, Burnaby, B.C. V5A 1S6 (Canada) (Received 23 August 1979) (Revision received 22 July 1980) (Accepted 1 August 1980) Summary We have found that formaldehyde is capable of inducing mutations in the nematode Caenorhabditis elegans. 4 concentrations of formaldehyde were tested. At a concentration of 1%, formaldehyde is lethal to the nematode, and 0.01% formaldehyde did not induce any mutations in approx. 60 000 tested chromosomes. 2 concentrations of formaldehyde, 0.1% and 0.07%, were found to be mutagenic, inducing both point mutations and deficiencies in the unc-22 region of linkage group IV. 4 of the point mutations have been demonstrated to be alleles of the unc-22 gene and have been mapped within the locus. 2 of the putative deficiencies have been confirmed. Each spans the unc-22 gene and at least 2 other genes in the region. A rough estimate of the forward mutation frequency using 0.1% formaldehyde in this region is 3 × 10 -s, while for 0.07% the frequency is 2 × 10 -4. Our laboratory is presently investigating the genetic organization and control of the unc-22 gene in Caenorhabditis elegans (Moerman and Baillie, 1979). As part of this program we are interested in examining the region around the unc- 22 gene to identify and characterize neighbouring genes. An essential part of this study is to generate a series of deficiencies in this region. Although X-rays can cause deficiencies in the nematode (Meneely and Herman, 1979), note was taken of the early results of Slizynska (1957) and the more recent findings of O'Donnell et al. {1977} demonstrating formaldehyde-induced deficiencies in Drosophila melanogaster. These observations led us to examine its mutagenic effects on the nematode. We report here that formaldehyde appears to be capable of inducing both point mutations and deficiencies in the nematode.