genes on the long arm of the human x are contained in the monotreme x and genes on the short arm of the human x are distributed on the autosomes of marsupials. ohno commented to the result that monotremes and marsupials were not considered to be ancestors of true mammals, but they have diverged very early from the main line of mammals. 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.