Evolutionary relationship between genes: Orthologs: Two copies of the same gene in two different species produced by speciation from a common ancestor. Paralogs: Two tandem copies of the same gene in the same genome due to a gene duplication event. Xenologs: Horitzontal transfer of genetic material between two species separated by a long evolutionary distance. Analogs: Two different genes from separated species that have converged on the same function by separate evolutionary paths.