The mechanisms by which sex is genetically determined are bewilderingly diverse and appear to change rapidly during evolution.(1) What makes the sex-determining process so prone to perturbations? Two recent articles(2,3) explore theoretically the role of genetic conflict in sex determination evolution. Both studies use the idea that selection on sex-determining genes may act differently in pare...

Sex determination is one of the most rapidly evolving developmental pathways, but the factors responsible for this fast evolution are not well resolved. The house fly, Musca domestica, is an ideal model for studying sex determination because house fly sex determination is polygenic and varies considerably between populations. Male house flies possess a male-determining locus, the M factor, whic...

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...

Mechanisms of vertebrate sex determination are reviewed in the light of what is known about the origin and evolution of sex chromosomes. All vertebrate males have testes that are similar in anatomy and in spermatogenesis. Despite a variety of sex chromosome systems, the same cascade of genes operate in the differentiation of testes and male genitalia. Only the primary signal or switch that init...

Sex determination is a fundamental process governed by diverse mechanisms. Sex ratio selection is commonly implicated in the evolution of sex-determining systems, although formal models are rare. Here, we argue that, although sex ratio selection can induce shifts in sex determination, genomic conflicts between parents and offspring can explain why single-factor systems (e.g. XY/XX or ZW/ZZ) are...

T he extraordinary diversity of sexdetermination mechanisms has long been noted. Many species resort to environmental cues for the determination of sex. A well known example is temperature-dependent sex determination in many (although not all) reptiles. Yet, many other species use genetic mechanisms, i.e., sex chromosomes, for the determination of sex. The beststudied systems of genetic sex det...

To identify the processes shaping vertebrate sex chromosomes during the early stages of their evolution, it is necessary to study systems in which genetic sex determination was recently acquired. Previous cytogenetic studies suggested that threespine stickleback fish (Gasterosteus aculeatus) do not have a heteromorphic sex chromosome pair, although recent genetic studies found evidence of an XY...

Some fishes mature and function as one sex and later transform to the other sex in response to social interactions. Previous evidence suggested that a change in developmental timing may be involved in the evolution of adult sex change in fishes. The most recent support for this idea came from reports that sex in the Midas cichlid, Amphilophus citrinellus, was determined by social conditions exp...

Sex determination is triggered by factors ranging from genotypic (GSD) to environmental (ESD), or both GSD + EE (GSD susceptible to environmental effects), and its evolution remains enigmatic. The presence/absence of sex chromosomes purportedly separates species at the ESD end of the continuum from the rest (GSD and GSD + EE) because the evolutionary dynamics of sex chromosomes and autosomes di...