For the last 25 years, Online Mendelian Inheritance in Animals (OMIA) has been providing free global access to an ever-increasing record of discoveries made by animal geneticists around the world. To mark this 25-year milestone, this document provides a brief account (including some pre-history) of how OMIA came to be; some timelines of important discoveries and advances in the genetics of the animal species covered by OMIA, gleaned from the OMIA database; and an analysis of the current state of knowledge regarding likely causal variants of single-locus traits in OMIA species, also gleaned from the OMIA database.