Overview of sex determination in mice. During mouse embryogenesis, bipotential gonads arise from the genital ridges by 10.5 days post-conception (dpc). In somatic cells of XY genital ridges, Sry expression (dark blue line at lower part of figure) starts at 10.5 dpc, reaches a peak at 11.5 dpc and then wanes by 12.5 dpc. A few hours later, Sox9 expression (light blue line at the lower part of the figure) is upregulated to induce differentiation of Sertoli cells. Sox9 expression peaks at 11.5 to 12.5 dpc, continues to be expressed postnatally and is supported by several positive-feedback loops (including fibroblast growth factor 9 (FGF9), prostaglandin D2 (PGD2) and SOX9 itself), and SOX9 subsequently activates many male-specific genes, including the gene encoding anti-Müllerian hormone (Amh). At 12.5 dpc, morphological differences between testis and ovary are evident. In the absence of SRY, genes such as Wnt4, Rspo1 and Foxl2 are expressed in a female-specific manner and induce ovarian development, as characterized by the expression of follistatin and many other ovary-specific genes. FOXL2, forkhead box L2; SOX9, SRY box containing gene 9; SRY, sex-determining region on the chromosome Y. This figure is adapted with permission from .