In biology, paralog [from the Greek paralogus = against logical expectation] refers to proteins of the same individual that occur simultaneously or sequentially in ontogenesis. Paralogous proteins have so many similarities in structure that they can be homologized (homology, sequence homology). An example of this are the α-, β-, γ-globins in mammals.
The paralogous molecules are encoded by paralogous genes. Paralogous genes are created by gene duplication (orthologous genes are created by specification). Paralogous proteins are therefore products of a gene family. They do not provide any information about the evolutionary development of molecules of a species (anagenesis).