Biological sex is described as three distinct, hierarchically-linked levels: genetic sex (XX/XY karyotype), gonadal sex (ovaries or testes), and phenotypic sex (external genitalia and secondary sexual characteristics), with each level determining the next through gene expression and hormone signaling. The presence or absence of the Y-linked SRY gene triggers a molecular switch (upregulating SOX9/FGF9 versus WNT4/RSPO1) that directs bipotential gonadal tissue toward testicular or ovarian fate, and gonadal hormone output (testosterone/DHT/AMH versus estrogen) subsequently drives differentiation of internal ducts and external genitalia. This is a concept within reproductive/developmental endocrinology and embryology, situating sex determination as a cascade from genotype to gonad to hormone-driven phenotype.
Biological sex is described as three distinct, hierarchically-linked levels: genetic sex (XX/XY karyotype), gonadal sex (ovaries or testes), and phenotypic sex (external genitalia and secondary sexua…