Literally meaning: “beside homolog”
Origin: Anc Greek
παρα-/para- (=beside, near, parallel)
λόγος/logos(=word, speech, discourse, reason)
The terms "ortholog" and "paralog" were coined in 1970 by American biologist Walter Fitch (1929 – 2011) in order to differentiate between different kinds of homology and different subsets of homologs. The homologous characters (genes and their products ) that are produced by speciation are called orthologs meaning “straight homology”. Homologous genes that are produced as gene duplication, which can occur within a lineage, in the absence of any speciation are called paralogs meaning “parallel homologs”.
Paralogs are genes related by duplication within a genome. Orthologs retain the same function in the course of evolution, whereas paralogs evolve new functions, even if these are related to the original one.