Orthologs are 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. (See also Paralogs.).
A gene with similar function to a gene in an evolutionarily related species. The identification of orthologs is useful for gene function prediction.
A homolog that has retained the same function as the sequence it is compared to, but in a different species. See also homolog, paralog, COG and GeneQuiz