Graves has discovered that these sixty or so genes are, in fact, remarkably conserved across all vertebrates. Birds, reptiles, amphibians and fish all have more or less the same set of genes as mammals for creating a testis or an ovary. What differs, however, is the master switch that kicks off the pathways. In the platypus this turned out to be one of the genes that’s in the orchestra and has stepped up to the front to trigger the whole sex-determination process. ‘SRY is just one way of kicking off the pathway, but you can do it by really almost any one of these sex-determining genes,’
