Phylogenetic tree and a proposed evolutionary scheme of ABCG family. Above: the proposed events in the evolution of the ABCG family. a, divergence of the half transporter with intron gain and loss, and the colored vertical bars in the NBD region represent conserved introns; b, divergence of the ABCG half transporter gene to give rise to each group, and possible formation process of ABCG full transporters (dash line). Below: part of tree from Figure 1 with introns locations of NBDs, the asterisk represent the root in the midpoint. Each group was marked as a line with the same color to the pane in b. The full transporter NBDs of ABCG are marked with a black pane in the phylogenetic tree; genes that have a Paramecium ortholog were marked with a blue ellipse.