Embryonic Development of the Gonad:
Primitive gonad (genital ridge) develops near a mesonephric duct and a paramesonephric duct, as paired thickenings of the coelomic epithelial layer that lines the body cavity, specifically in the region that overlays the surface of the mesonephros. Bipotential gonad, that able to adopt either male or female fate, is the first sign of development of the reproductive organs, which appears in mouse at around E10.5. The gonadal ridge continues to grow and form primary sex cords (ovigerous/testis cords) within it. Development of a testis (male) or an ovary (female) is triggered by the expression and proper function of Sry, the testis-determining gene. The primary sex cords in the male will eventually mature to become the sperm-nurturing seminiferous tubules. In the female, the primary sex cords will contribute to nurturing tissue of developing ova.
The gonad consists of germ cells and somatic cells. The primordial germ cells (PGCs) do not arise within the genital ridge. The precursors of the PGCs originate in the mouse epiblast at E6–6.5. The PGCs migrate from the base of the allantois via the gut mesentery and populate the bipotential gonad at around E10.5-11.5. The somatic cells originate from mesonephros and coelomic epithelium.