b chromosomes have a functional effect on female sex determination in lake victoria cichlid fishesb染色体功能影响女性性别决定在维多利亚湖丽鱼科的鱼.pdf

B Chromosomes Have a Functional Effect on Female Sex Determination in Lake Victoria Cichlid Fishes 1 1 1 1 1 Kohta Yoshida , Yohey Terai , Shinji Mizoiri , Mitsuto Aibara , Hidenori Nishihara , Masakatsu 1¤ 2 3 3 4 1 Watanabe , Asato Kuroiwa , Hirohisa Hirai , Yuriko Hirai , Yoichi Matsuda , Norihiro Okada * 1 Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan, 2 Laboratory of Animal Cytogenetics, Faculty of Science, Hokkaido University, Sapporo, Japan, 3 Primate Research Institute, Kyoto University, Inuyama, Japan, 4 Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan Abstract The endemic cichlid fishes in Lake Victoria are a model system for speciation through adaptive radiation. Although the evolution of the sex-determination system may also play a role in speciation, little is known about the sex-determination system of Lake Victoria cichlids. To understand the evolution of the sex-determination system in these fish, we performed cytogenetic analysis in 11 cichlid species from Lake Victoria. B chromosomes, which are present in addition to standard chromosomes, were found at a high prevalence rate (85%) in these cichlids. In one species, B chromosomes were female- specific. Cross-breeding using females with and without the B chromosomes demonstrated that the presence of the B chromosomes leads to a female-biased sex ratio in this species. Although B chromosomes were believed to be selfish genetic elements with little effect on phenotype and to lack pro