Fig. 11
From: Rapid divergence of a gamete recognition gene promoted macroevolution of Eutheria
Zan ontogeny. In this proposed ontogeny, Zan and ZanL evolve from an ancient progenitor in a stem vertebrate, with the syntenic region of the progenitor comprising in part at least two genes present in progressively conserved Zan and ZanL syntenic loci of extant species. The ZanL descendant persists in ray- and lobe-finned fish and in reptiles (black branches) but is lost in amphibians, birds, and marsupials (dotted branches). ZanL also persists in Prototheria (monotremes) after divergence of the therian crown group but is lost in Metatheria (marsupials) after divergence from Eutheria, whereas authentic Zan evolves in the latter (blue branch) as a consequence of its neofunctionalization to a sperm-egg recognition molecule