This paper is part of the ongoing efforts within the framework of the Open Biomedical Ontologies (OBO) ontology library to optimize the treatment of relations in biomedical informatics. When ovum and sperm fuse to form a zygote, then the latter is derived from the former. This derives_from relation is of huge importance not only in embryology but also in every other science dealing with ontogenetic processes. This study examines critically the treatment of derives_from in the OBO Relation Ontology in light of its conformity to the underlying processes of development and transformation in biological and medical reality.