The schematic genomic structure of RHOXF2 gene copies in humans (a) and chimpanzees (b). (a) There are two 48.9-Kb segmental tandem repeats containing two copies of the RHOXF2 gene, i.e. RHOXF2 and RHOXF2b in the human genome. (b) Three segmental tandem repeats containing three copies of RHOXF2 gene are constructed for chimpanzees according to the three known BAC (bacterial artificial chromosome) clones (281C1, 349N3 and 565A12) of a male chimpanzee (CHORI251). The black triangles indicate endogenous retrovirus (ERV) sequences flanking the breakpoints.