Sign Up. In some species, including most mammals and insects, sex is determined solely by chromosomes; in other species, sex is a matter of environmental conditions. Turtles of the World. In this case—which governs all snake species—males are the homogametic sex ZZ and females are the heterogametic sex ZW.
It has been proposed  that temperature acts on genes coding for such steroidogenic enzymesand testing of homologous GSD pathways has provided a genic starting point. One remarkable finding is that the injection of an aromatase inhibitor into the eggs of an all-female parthenogenetic species of lizards causes the formation of males Wibbels and Crews
After depositing the eggs, the mother returns to the water, but remains close to protect the eggs through the entire incubation period, which lasts about three months. Journal Information Scientific Reports 5, Article number: doi This model indicates that there is no genetic predisposition for the embryo of a temperature-sensitive reptile to develop as either male or female, so the early embryo does not have a "sex" until it enters the thermosensitive period of its development.
What causes a sea turtle to be born male or female? This paradigm, though, has been recently challenged, with new evidence now emerging that there may indeed be both sex chromosomes and temperature involved in the sex determination of some reptile species.
In most species, gender is determined during fertilization.
Professor Taisen Iguchi said, "Organisms that have adopted TSD systems may be more susceptible to the risks of environmental change, such as global warming. In the case of some Costa Rican American crocodile Crocodylus acutus populations, the high temperatures are already affecting the gender ratio.
Already a subscriber? Research shows that if a turtle's eggs incubate below
Another hypothesis is that aromatase activity may be regulated by Sox9. The estrogen synthesis inhibitors used in the experiments mentioned above worked by blocking the aromatase enzyme, showing that experimentally low aromatase conditions yield male offspring. This is the first demonstrated report of a biomolecule associated with regulation of the very unique temperature-dependent sex determination mechanism.
NILE CROCODILE: Temperature Dependent Sex Determination: The Pulse of the Planet daily radio program offers free legal online mp3 downloads, exploring the world of sound in nature, culture and science, with audio adventures, world music, extraordinary sound portraits, science diaries, and nature ring-tones; an amazing sonic experience.