Figure 1

Phylogenetic relationships between the species used in this study. The number of Irx and Mkx genes in each genome and the potential clustering of the Irx genes are indicated. '+' indicates that the Irx genes form one or more clusters, '-' indicates that there is no clustering, '?' indicates that the current state of the assembly of the genome of the corresponding species does not allow determination of the existence of clusters, and '/' indicates cases where there is only a single Irx gene. The names of representative phylogenetic groups are indicated on the left of the nodes that define these different groups and along some of the terminal branches. The identification of Irx genes in some of the indicated species were already reported in other studies and our data are in full agreement with the previously published ones [4, 5, 9, 11–13, 37]. The color code for some of the metazoan evolutionary lineages (sponges, cnidarians, placozoans, trochozoans, deuterostomes, and ecdysozoans) will also be used in the next figures.