Mammalian genital ridge is:
Mammalian gonad primordium arises from intermediate mesoderm and overlying coelomic epithelium during fourth to fifth week, forming paired genital ridges on ventromedial surface of mesonephros. These ridges remain morphologically undifferentiated and molecularly bipotential, capable of becoming either testes or ovaries. Supporting precursors co-express Wt1, Sf1, Gata4, Lhx9 and low Sox9 and Wnt4 maintaining plasticity. Decision depends on transient Sry upregulating Sox9 in XY or Rspo1/Wnt4/β-catenin signaling in XX. Bipotential state allows mutual antagonism between male and female programs determining final fate.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Formation of bipotential gonad and sex determination.