Genome evolution in the Paramecium phylum. Three WGDs occurred during the evolution of the Paramecium phylum (Aury et al. 2006). The OWGD, IWGD, and RWGD gave rise to here named old, intermediate, and recent genomes, respectively. Genes from the ancestral genome gave rise to ohnolog sets (OHSets) of 1–23 members in the P. tetraurelia genome, depending on the timing and number of the deletion and retention events respectively schemed by open and closed circles. In this example, one gene duplicate has been deleted from the old genome following the OWGD and another one from the intermediate genome, following the IWGD. As a consequence the corresponding P. tetraurelia OHSet only includes two members.
