Homology that arises through speciation.

Genes and their cognate proteins that arise in different species but are derived from a common ancestor. Orthologous proteins may not have the same function from species to species. Bioinformatics techniques can identify orthologous proteins based on gene and protein sequences and are useful for helping identify unknown proteins. See also Conformation, Conservation, Domain, Homology, Paralogy.

True homology of molecular sequences, i.e. descended in toto from the same ancestral sequence. Orthologous sequences exist in only one copy per organism, and can accurately reflect the phylogenetic relationships of species (cf. paralogy, plerology, xenology).

The right description of things.