Homologous, Orthologous and Paralogous Genes


Orthology and paralogy are two different types of homology, depending on whether the genes in question derive from a duplication event or a speciation event.

Keywords: common ancestry; gene duplication; speciation

Figure 1.

Orthologous and paralogous genes. Genes A and B were derived from a duplication event and so are paralogous. Gene A in species 1 and gene A in species 2 were derived from a speciation event and are orthologous, and so are gene B in species 1 and gene B in species 2.

Figure 2.

Green and red pigment genes in humans, apes and Old World monkeys were derived from a duplication event in the common ancestor of these organisms. So, human green and red pigment genes are paralogous, while human and rhesus monkey green pigment genes are orthologous and so are human and rhesus monkey red pigment genes.



Fitch WM (1970) Distinguishing homologous from analogous proteins. Systematic Zoology 19: 99–113.

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Li, Wen‐Hsiung(Jul 2006) Homologous, Orthologous and Paralogous Genes. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0005297]