Growth rate differs considerably between temperatures that promote formation of 100%ovaries (32–33°C) and testes (26– 27 °C), respectively. When exogenous E2 are given near the pivotal temperature (29–30 °C), production of endogenous estrogens is initiated. Thus, a minimal dose of exogenous estrogens (or endocrine-disruptors) are required for ovarian formation (Sheehan et al., 1999) without apparent alteration the fine balance between growth and ovarian differentiation. However, the molecular pathways involved in ovarian determination by FPT are always modified (Ramsey and Crews, 2007) (Fig. 11).