The absence of recombination between Y and X has allowed for the development of important differences in function between some Y and X paralogs, such as the oncogenic functions of testis-specific protein Y–encoded (TSPY) versus the tumor suppressor function of its paralog, testis-specific protein X–encoded (TSPX) (54) or the differences in demethylase activity between KDM6A and its paralog, UTY (55). This evidence concerns the gene KDM6A and neoplasm.