Common Spontaneous Sex-Reversed XX males of the Medaka Oryzias latipes

Common Spontaneous Sex-Reversed XX males of the Medaka Oryzias latipes

Indrajit Nanda^a, Ute Hornung^b, Mariko Kondo^b, Michael Schmid^a, and Manfred Schartl^a
^a Institute for Human Genetics, Biocenter, University of Würzburg, D-97074 Würzburg, Germany
^b Department of Physiological Chemistry I, Biocenter, University of Würzburg, D-97074 Würzburg, Germany

Corresponding author: Manfred Schartl, Biocenter, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany., phch1{at}biozentrum.uni-wuerzburg.de (E-mail)

Communicating editor: D. J. GRUNWALD

In the medaka, a duplicated version of the dmrt1 gene, dmrt1bY,has been identified as a candidate for the master male sex-determininggene on the Y chromosome. By screening several strains of Northernand Southern medaka we identified a considerable number of maleswith normal phenotype and uncompromised fertility, but lackingdmrt1bY. The frequency of such males was >10% in some strainsand zero in others. Analysis for the presence of other Y-linkedmarkers by FISH analysis, PCR, and phenotype indicated thattheir genotype is XX. Crossing such males with XX females ledto a strong female bias in the offspring and also to a reappearanceof XX males in the following generations. This indicated thatthe candidate male sex-determining gene dmrt1bY may not be necessaryfor male development in every case, but that its function canbe taken over by so far unidentified autosomal modifiers.

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