Sex-determination mechanisms vary greatly among taxa. It has been proposed that genetic sex-determination pathways evolve in reverse order from the final step in the pathway to the first step. Consistent with this hypothesis, doublesex (dsx), the most downstream gene in the Drosophila sex-determination cascade that determines most sexual phenotypes also determines sex in other dipterans and the...

Most animals are male/female species and reproduce sexually. Variation in this pattern of reproduction has arisen many times during animal evolution, particularly in nematodes. Little is known about the evolutionary forces and constraints that influenced the origin of self-fertilization, for instance, a type of reproduction that seems to have evolved many times in the phylum Nematoda. Caenorhab...

E volutionary developmental biology is motivated by the premise that the differences we see between species are caused by changes that have occurred in the genes that regulate their developmental programs. Beginning in the 1980s, general principles began to emerge about the evolution of development in animals. The identifi cation of the Hox genes in Drosophila melanogaster and the subsequent di...

The endemic cichlid fishes in Lake Victoria are a model system for speciation through adaptive radiation. Although the evolution of the sex-determination system may also play a role in speciation, little is known about the sex-determination system of Lake Victoria cichlids. To understand the evolution of the sex-determination system in these fish, we performed cytogenetic analysis in 11 cichlid...

Sex chromosomes in dioecious and polygamous plants evolved as a mechanism for ensuring outcrossing to increase genetic variation in the offspring. Sex specificity has evolved in 75% of plant families by male sterile or female sterile mutations, but well-defined heteromorphic sex chromosomes are known in only four plant families. A pivotal event in sex chromosome evolution, suppression of recomb...

That sex determining systems ever change is paradoxical but can be explained by noting that conflict between selfish elements and their modifiers will often cause a shift in sex determining strategy. The evolution of the novel sex determining system of moles (Talpa europaea and T. occidentalis) may, we argue, be an example of just such a process. Three different models for the evolution of fema...