The extraordinary diversity of sex-determining mechanisms found in nature is thought to have arisen by the addition, modification or replacement of regulators at the upstream end of the sex-determining pathway. The spread of a novel regulator of sex determination can manifest itself by an evolutionary transition between environmental and genetic sex determination, for example, or between male a...

A combination of analytical and simulation models is used to explore the initial evolution of genic sex determination from polygenic sex determination. Prior studies have indicated that polygenic sex determination is rare or absent in extant species but that it has likely played an important intermediate role in the evolution of other genetic sex-determination systems. This study explores why p...

A surprising diversity of mechanisms controls sex determination of vertebrate organisms, even among closely related species. Both genetic and temperature-dependent systems of sex determination have been described in teleost fish. In the common zebrafish model organism, heteromorphic sex chromosomes are not observed, and the potential role of a genetic component of sex determination remains larg...

In reptiles, sex-determining mechanisms have evolved repeatedly and reversibly between genotypic and temperature-dependent sex determination. The gene Dmrt1 directs male determination in chicken (and presumably other birds), and regulates sex differentiation in animals as distantly related as fruit flies, nematodes and humans. Here, we show a consistent molecular difference in Dmrt1 between rep...

The sex of a reptile [6] embryo partly results from the production of sex hormones [7] during development, and one such process to produce those hormones [8] depends on temperature of the embryo's environment. The production of sex hormones [7] can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination [9], also ca...

In this review, we describe the history of amniote sex determination as a classic example of Darwinian evolution. We suggest that evolutionary changes in sex determination provide a foundation for understanding important aspects of chromosome and genome organization that otherwise appear haphazard in their origins and contents. Species with genotypic sex determination often possess heteromorphi...

The sex of a reptile [6] embryo partly results from the production of sex hormones [7] during development, and one such process to produce those hormones [8] depends on temperature of the embryo's environment. The production of sex hormones [7] can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination [9], also ca...

The sex of a reptile [6] embryo partly results from the production of sex hormones [7] during development, and one such process to produce those hormones [8] depends on temperature of the embryo's environment. The production of sex hormones [7] can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination [9], also ca...