Ohno's law was proposed by a Japanese-American biologist Susumu Ohno, saying that the gene content of the mammalian species has been conserved over species not only in the DNA content but also in the genes themselves.
[1] Mammalian X chromosomes in various species, including human and mouse, have nearly the same size, with the content of about 5% of the genome.
Moreover, X-autosome translocation would have been prohibited because it might have resulted in detrimental effects for survival to the organism.
Thus in mammals, the content of X chromosomes has been conserved after typical 2 round duplication events at early ancestral stages of evolution, at the fish or amphibia (2R hypothesis).
[4] Chloride channel gene (CLCN4) was mapped to the human X but on chromosome 7 of C57BL/6 mice, species of Mus musculus, though the gene is located on X of Mus spretus and rat.