The genetic map of C. elegans shows clearly defined clusters of genes on the autosomes. Brenner (1974) suggested the possibility that these clusters might be produced by a lower frequency of recombination in a defined region of a chromosome. In D. melanogaster, treatment with ionizing radiation (and other factors) results in large increases in recombination frequency across centromeric regions primarily. These increases in recombination frequency have been termed 'radiation induced map expansion'. We have investigated the occurrence of radiation induced map expansion in C. elegans. Previously, some of the factors that alter recombination frequency in the
dpy-5 of linkage group I were examined ( temperature, parental age, and
rec-1, for example). Currently, we have investigated the effect of gamma radiation on recombination in this interval. We found that treatment with gamma increases: recombination frequency two to three-fold, nondisjunction eight-fold, and F1 sterility from 0 to 14%. We are further investigating the sensitivity of different meiotic stages. The existence of 'map expansion' in the
dpy-5 which corresponds to the region of the cluster on linkage group I), implies that recombination in this region can occur more frequently than it does in control strains. One possibility is that recombination frequency in this region is 'normally' reduced (as proposed by Brenner). We are investigating this phenomena for other regions of linkage group I.