Figure 5. The molecular evolution of KANK genes and the origin of vertebrate blood vessels.

The phylogenetic relationships of bilateria and vertebrata are based on the recent phylogenomic analyses and our past collagen gene phylogenetic analyses. The branch lengths are not proportional to the time of diversification. The two vertical dark blue bars on the tree indicate the WGD events (R1 and R2) at the origin of the vertebrates. The other light blue vertical bar represents the teleost specific WGD. The green bar on the bird lineage indicates the loss of KANK2. The process of KANK gene duplication and diversification through WGD is illustrated by the brown bars. The co-option of the vertebrate four KANK genes’ expression coincides with the vertebrate vascular vessels.