Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Changing Sexes
Name: Michael
Status: Student
Grade:  Other
Location: NV
Country: United States
Date: Summer 2009

What do you call the ability of an animal, say a Frog, to BE either sex? Is that asexuality? We know there are many factors that determine why a Frog might be male or female but what do you call the ability to be either sex?? This happens only in fish and frogs and maybe snakes?

Hi Michael,

Gender in frogs is fixed - a frog cannot change its gender during its life. Once a male always a male.

Some fish on the other hand can and do change gender. Australia's Barramundi is not only very good eating, but it is also hermaphrodite. (From Greek - Hermes and Aphrodite - a male and a female god) It carries both male and female genitalia, but different parts work at different parts of its life. All small barramundi are males, and they get to chase and impregnate as mane females as they can. Later they become female, and become the subject of all that male attention. Poetic justice I say.

All snails and earthworms are also true hermaphrodites - when they mate BOTH snails become pregnant!

In many reptiles gender is not fixed by genetics, but is determined during early development. Crocodiles, alligators, turtles and some other reptiles are all gender determined by temperature during incubation. In crocodiles, an all-male brood typically results from nest temperatures in the range of 32 to 33 degrees Celsius ( roughly 89 - 91F). When the incubation temperature moves outside this range either above or below, the result is female crocodiles -- an overabundance of them. Among turtles, the ideal temperature between 28 and 29C produces an even mix of males and females. Too high a temperature leads to more females again. Cooler temperatures favour the males. In New Zealand the Tuatara - a so-called 'living fossil' - produces more males as the temperature of the brood chamber increases. Recent studies show that only one degree celsius is enough to shift the balance. There is now a concern that global warming may lead to too many female crocodiles and turtles, and no males to fertilize their eggs. Scientists in New Zealand are already finding too many male tuatara. If this were to happen for an extended period, we would see the extinction of many reptile species.

For more information the following article goes into more detail. reptiles

Nigel Skelton
Tennant Creek High School

Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory