From Biology-Online Dictionary | Biology-Online Dictionary

Science (genetics, molecular biology, genomics) genes or gene products that are homologous (descended from a common ancestor) and are found in separate species due only to the speciation event (not to gene duplication). For example human hemoglobin alpha is orthologous to horse hemoglobin alpha, but is paralogous to both human and horse hemoglobin beta.

Compare: homology, paralogy