Although mammalian hybrids have been known for centuries3, studies of the genetic and cellular bases of hybrid sterility in mammals are surprisingly scarce. Several genes causing male sterility in hybrids between karyotypically identical species of the house mouse (Mus musculus x M. domesticus)5678 and felines (Felis catus x Profelis serval, F. catus x Prionailurus bengalensis)9 have been localised and sequenced. One of them, PRDM9 (referred to as a speciation gene), is involved in the control of DSB formation10. Male sterility or reduced fertility accompanied by synaptic aberrations of autosomes and sex chromosomes has been widely reported in hybrids of chromosomally divergent mammalian species, subspecies and local populations3111213141516171819.