The Herpetological Journal

pp.122-125

Authors: William H. N. Gutzke

Abstract: Sex determination and sexual differentiation in vertebrates have received a great deal of attention in the past few decades. The current view is that gonochorism (separate sexes) in the earliest vertebrates involved environmental control of sex determination and that genotypic sex determination evolved later (lntersexuality in the Animal Kingdom, 438, 1 975). Concurrent with the establishment of the latter was the gradual evolution of sex chromosome heteromorphism. Reptiles are excellent models for investigations focusing on sex determination' and sexual differentiation because they exhibit: (a) both genotypic and environmentally-determined sex determination, (b) various degrees of sex chromosome heteromorphism, ( c) both male and female heterogamety (the former also occurs in mammals, the latter in birds), and (d) variations from the typical I: 1 sex ratio predicted by Fisher (The Genetical Theory of Natural Selection, 1 930). This paper will review patterns of sex determination for the various groups of reptiles and will briefly discuss physiological mechanisms that may be regulating sexual differentiation.