Forces driving the development of the WPO. Curation of C. elegans literature helps to increase the robustness of the phenotype ontology and we create terms as needed. Ontology views within OBO-Edit. (a) Blue lines point to the reference for the term. In some cases more than one term is created from a single reference [9, 66–71]. (b) Expert input leads to extensive granularity in the ontology. There are 29 descendants of the 'pronuclear nuclear appearance defective early emb' branch (bracketed box), which was refined by soliciting feedback from the community.