Figure 7.

Model of mammalian A3 gene evolution. The model proposes the presence of several A3 genes in Placentalia before the separation of the super-orders Afrotheria, Xenarthra, Euarchontoglires and Laurasiatheria. According to the phylogenetic relationships among the extant A3 proteins, a host-specific evolution of the A3 genes during the early evolution of the Placentalia orders by means of preservation, deletion and/or gene duplication and concomitant subfunctionalization or neofunctionalization is inferred. Successive duplication events from a single ancestral A3 gene might have generated multiple A3 genes before basal radiation within Placentalia. The divergence times of taxons is in millions of years (Myr) ago. Basal radiation within Monotremata and Marsupialia is not shown. A3, APOBEC3; A3Δ5, A3 lacking exon 5 derived amino acids. Relationship of taxa and timing of mammalian evolution is based on [85], but please note that the timing is controversial [86]. The study of Wible et al. [87] supports a later diversification of the placentalia superorders following the Cretaceous-Tertiary (K/T) boundary 65 million years ago.