an autosome to the Y chromosome. In 1999, Page and his then-graduate student Bruce Lahn showed that the X and Y chromosomes had diverged in four steps, beginning 200-300 million years ago. Later cross-species comparisons would show that while ancestral genes on the Y chromosome initially underwent rapid decay, the remaining genes have remained stable for the last 25 million years, overturning the long-held view that the Y chromosome was going extinct. In a 2014 study, Page concluded that the conserved genes on the Y chromosome played an important role in male viability, since they were dosage-dependent genes with similar but not identical counterparts on the X chromosome that all have regulatory roles in transcription, translation, and protein stability. Because these genes are expressed throughout the body, Page further concluded that these genes give rise to differences in the biochemistry of male and female tissues. In super-resolution studies of the sex chromosomes, Page has found evidence of an evolutionary "arms race" between the X and Y chromosomes for transmission to the next generation. In one study, Page found that human X and mouse Y chromosomes have converged, independently acquiring and amplifying gene families expressed in testicular germ cells. Another study found that the mouse Y chromosome had acquired and massively amplified genes homologous to the testis-expressed gene families on the mouse X chromosome. The genetics of germ cells Page used the mouse as a model to study the genetics of meiotic initiation, showing that retinoic acid (RA) is the key factor which induces meiosis, as well as identifying several important genes crucial to the meiotic initiation pathway, including Stra8 and DAZL. Page further discovered that the differentiation germ cells into gametocytes (oocytes in females or spermatocytes in males) does not depend on meiotic initiation, as commonly thought, showing that germ cells deficient in Stra8, a gene that activates the meiotic pathway, are still capable of growth and differentiation. Awards and honors His honors and awards include: 1986 MacArthur Prize Fellowship 1989 Searle Scholar Award 1997 Francis Amory Prize, American Academy of Arts and Sciences (for genetic studies of mammalian sex determination; prize shared with Peter Goodfellow and Robin Lovell-Badge) 2003 Curt Stern Award, American Society of Human Genetics (for outstanding scientific achievement in human genetics) 2005 Member, National Academy of Sciences 2007 Fellow, American Association for the Advancement of Science 2008 Member, National Academy of Medicine 2011 Fellow, American Academy