CHANGING MASTER GENES. “Even more intriguingly, the master sex-determining gene itself can change; and depending on the type of change, this has different chromosomal consequences. If for example, the function of a gene as a male sex-determining gene is turned over to a different gene, which resides nearby on the same chromosome as the previous master gene, there is no change of the Y chromosome (homologous turnover).”
http://www.pnas.org/content/112/34/10575.full