Temperature-dependent sex determination(TSD) has been studied extensively over the past several decades in a variety of reptiles.Sexual differentiation of gonads is sensitive to temperature during thermosensitive period(TSP).Two patterns have been demonstrated in chelonians: ① males from cool temperature while females from warm temperature(TSD Ⅰa) and ② females from both cool and warm temperatures,while males from intermediate temperature(TSD Ⅱ).The possible mechanisms of TSD caused by sex steroid hormone levels have been studied.Several groups have provided direct support for the hypothesis that the physical stimulus of temperature is transduced into an endocrine signal that directs the sex-determination process: specifically,estrogens and their precursors,aromatizable androgens,stimulate the female-determining cascade and inhibit the male determining cascade.Preliminary results show that expression of Sf1,Mis,Sox9,Dax1,Wt1 and Dmrt1 is affected by temperature,which may be involved in sex determination..Hypotheses on the evolutional significance of TSD are introduced,and each of these explanations remains partly but not fully plausible.