BRUNER, A.M.*; ROSS, J.A.; PEICHEL, C.L.; Fred Hutchinson Cancer Research Center; University of Washington; Fred Hutchinson Cancer Research Center: The evolution of sex determination in stickleback fish

Sex determination pathways should be highly conserved, yet they can diverge even between closely related species. The stickleback family, Gasterosteidae, provides an opportunity to investigate the mechanisms that underlie rapid evolution of sex determination pathways. The three-spine stickleback, Gasterosteus aculeatus, does not have cytogenetically visible sex chromosomes, but linkage analysis and genomic studies indicate that it does have a young XY sex determination system. Its closest relative, Gasterosteus wheatlandi, has a cytogenetically visible XY chromosome pair. These species are only 20 million years diverged from Apeltes quadracus, which has a cytogenetically visible ZW chromosome pair. How did members of Gasterosteidae evolve different sex chromosomes in an evolutionarily short period of time? How have the pathways of sex determination diverged in these species? Which genes arose to control sex determination and what mechanisms contributed to this process? With the development of genetic and genomic tools in G. aculeatus, we have begun to investigate the evolution of stickleback sex determination. I will present our work to isolate the master sex-determining locus of the three-spine stickleback, G. aculeatus, as well as comparisons of genetic markers on the sex linkage groups among the closely related members of the family Gasterosteidae.