Evolution of the family of class II histone deacetylases (HDACs) followed the 2R model. The HDAC family (TF106174) is the family of class II histone deacetylases, which include four vertebrate genes: HDAC4 (located on chromosome 2), HDAC5 (located on chromosome 17), HDAC7 (chromosome 12) and HDAC9 (chromosome 7). There are only single genes for class II histone deacetylases in each C. intestinalis (hda4), fly (HDAC4) and worm (hda-4). Red node dots signify duplication nodes, while green node dots signify speciation nodes. Labels "Vertebrata (2R)" signify nodes corresponding to 2R-WGD.