X indicates gene duplication.
So speciation comes here before duplication. For example Koonin et al. By contrast, paralogs are homologous genes that have evolved by duplication and code for protein with similar, but not identical functions. Indeed, the phylogenetic analysis allows one to determine orthology relationships but not functional equivalence . The case of lactate dehydrogenase Let's now take the reverse situation of two closely related genes in one organism that ahve been the result of a duplication before a speciation event occurred, e.g. those of mammalian lactate dehydrogenase isoenzymes.