Ortholog

Ortholog

An Ortholog is a term used in genetics to refer to genes in different species that evolved from a common ancestral gene by speciation. Normally, orthologs retain the same function in the course of evolution. Identification of orthologs is critical for reliable prediction of gene function in newly sequenced genomes.

History

The concept of orthology was introduced in 1970 by Walter Fitch. Fitch originally defined orthology as those homologous sequences that are descended from an identical ancestral sequence. The concept of orthology is central to most computational approaches to functional annotation.

Function

Orthologs, or orthologous genes, are very important in the sense that they can be used to predict the function of a gene in a newly sequenced genome. If two genes in different organisms are orthologous, they are presumed to have the same function.

Identification

Orthologs can be identified using phylogenetic trees, but also through simple reciprocal best hits in BLAST searches. Several databases provide orthology predictions, including OrthoDB, InParanoid, EggNOG, and OrthoMCL.

See also

• Paralog
• Homology (biology)
• Convergent evolution
• Horizontal gene transfer

References

Ortholog Resources
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