Studying the forces that drive the evolution of sex determination has mainly come from theoretical works, with little empirical data. Reptiles in which both incubation temperature and sex chromosomes interact to determine sex may represent "transitional" evolutionary states between two end points: complete GSD and complete TSD.
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Bioessays 27 : — Perrin N What uses are mating types? In contrast, germ cells in Drosophila  and mammals  receive signals from the surrounding somatic gonad, but they also make an autonomous decision during germ line sexual development; this may also be true for chickens .
There is some empirical evidence for the repeated use of the same master sex determination switch genes in animals. Biochem Genet 47 : 66—
Heteromorphic sex chromosomes: sex chromosomes that are morphologically distinct. Expression of Sry early in embryonic development initiates testis differentiation by activating male-specific developmental networks, while in its absence, ovaries develop.
Such constraints largely explain why sexes at the gametic level are two and only two, and why anisogamy independently evolved in many lineages. The simulations were used to study natural conditions and to predict future outcomes in the most accurate way for the understanding of TSD mechanisms in sea turtle populations.
Abstract Sexual reproduction is an ancient feature of life on earth, and the familiar X and Y chromosomes in humans and other model species have led to the impression that sex determination mechanisms are old and conserved. Bachtrog D The temporal dynamics of processes underlying Y chromosome degeneration.
Gynandromorphs: individuals that contain both male and female characteristics. Sex determination can occur in different forms, such as genetic sex determination GSD and environmental sex determination ESD , depending on the species of the organism.
Nat Genet 46 : — This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
Walker G Sex determination in the larvae of the parasitic barnacle Heterosaccus lunatus : an experimental approach. In a study directed by Francesc Piferrer, from the Institute of Marine Sciences in Barcelona, published in the open-access journal PLoS ONE on July 30, the Spanish researchers used field and laboratory data to critically analyze the presence of TSD in the 59 species of fish where this type of sex determining mechanism had been postulated.