Practice question

When Y chromosome absent, testis-inducing pathway cannot be triggered due to lack of Sry. Bipotential supporting precursors therefore default to ovarian trajectory driven by active Wnt4/Rspo1/β-catenin axis. In XX gonads Rspo1 sensitizes Frizzled receptors to Wnt4, inhibits β-catenin destruction complex allowing nuclear accumulation. Nuclear β-catenin activates Foxl2, Follistatin and Dax1 while repressing Sox9 and Fgf9, blocking Sertoli and Leydig differentiation. Consequently ovary forms containing granulosa cells and meiotic germ cells. Thus absence of Y chromosome indirectly activates pro-ovarian Wnt/β-catenin cascade that specifies female gonad.