HOMOLOGS. “In mammals, only a few X-linked genes have homologues on the Y chromosome, and several Y-linked genes are known that do not have homology to X-linked genes and have presumably been translocated to the Y from elsewhere; in D. melanogaster, all known Y-linked genes are in this latter category.”
http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html