My TA mentioned these three mutations of C. elegans since we started working with the worms but seems to skip over what the differences are...
Dpy is a class of genes. Usually they're written in lowercase when referring to a mutant allele. The name Dpy itself stands for dumpy and comes from the morphological change that occurs when one or more of the genes are mutated: the worms appear short and fat, or dumpy.
Another big class is Unc. Mutations in those genes cause uncoordinated movement.
For a description of the genes, see http://www.wormbase.org