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Updated: May 27, 2026

Dissection of Larval Zebrafish Gonadal Tissue
Published on: April 26, 2017
The end of gonad-centric sex determination in mammals
1Department of Integrative Biology & Physiology, Laboratory of Neuroendocrinology of the Brain Research Institute, University of California, Los Angeles, CA 90095-7239, USA. arnold@ucla.edu
Abstract:
The 20th-century theory of mammalian sex determination states that the embryo is sexually indifferent until the differentiation of gonads, after which sex differences in phenotype are caused by the differential effects of gonadal hormones. However, this theory is inadequate because some sex differences precede differentiation of the gonads and/or are determined by non-gonadal effects of the sexual inequality in the number and type of sex chromosomes. In this article, I propose a general theory of sex determination, which recognizes multiple parallel primary sex-determining pathways initiated by genes or factors encoded by the sex chromosomes. The separate sex-specific pathways interact to synergize with or antagonize each other, enhancing or reducing sex differences in phenotype.
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