DETERMINATION AND DIFFERENTIATION OF SEX IN REPTILES : A KEY ROLE FOR AROMATASE

摘要

In many species of reptiles sex is determined by zygotic sex chromosome composition. This so-called genotypic sex determination (GSD) obeys either male heterogamety (male XY, female XX) or female heterogamety (female ZW, male ZZ), with sex chromosomesvarying from homomorphic to strongly heteromorphic. In other reptilian species, the sexual differentiation of gonads is dependent on the incubation temperature of eggs during a critical period of embryonic development (temperature-dependent sex determination, TSD). These species do not display heteromorphic sex chromosomes. A ZW/ZZ mechanism of GSD is observed in all snakes. Both GSD (XY/XX or ZW/ZZ) and TSD systems exist in lizards and turtles. TSD has been found in all crocodilians so far studied (half of the species) and the two extant species of Sphenodon (Crée et al., 1995 ; reviewed by Pieau et al., 1995 and Pieau, 1996).