The human-specific DUX4 clusters. Figure is not to scale. See figure for a guide to colours, Figure 1 for a guide to symbols and Figure 1 legend for notes on naming. The two DUX4 clusters found at the q-telomeres of human chromosomes 4 and 10 have no equivalent in mouse. Both regions are flanked by synteny or paralogy breakpoints. The chromosome 4 cluster, with the two, unrelated, FRG genes, is most likely the ancestral cluster, which duplicated and rearranged to form the chromosome 10 cluster with one FRG gene and the other FRG copy on chromosome 20. Another copy of the FRG2 section, without the distal DUX4L duplications, is present on chromosome 3. There are many more copies of FRG1, FRG2, TUBBB, FAM166A and the other genes from the chromosome 4 cluster in other regions of the genome, some of which are shown here; almost all duplicates can be found in subtelomeric and pericentromeric regions and where it relates to the genes on chromosome 4, those duplicates are subsets of the chromosome 4 arrangement.