Schematic showing possible intertaxa relationships for a hypothetical gene family that is found in two taxa, T and U, that shared a last common ancestor (LCA) in which two paralogs of the gene, A and B, were already present as a consequence of a gene duplication that predates the speciation, after which sequences within lineages T and U diverged independently. A
represent true orthologs. Pair BT 1and BT 2represent paralogs. Other pairs of modern proteins are neither orthologs nor paralogs.