Final answer:
The temperature during development regulates the genes that determine the sex of a red-eared slider turtle.
Step-by-step explanation:
The environmental factor that regulates whether genes that determine the sex of a red-eared slider turtle are turned on or off is the temperature during development. The sex determination in red-eared slider turtles is influenced by the incubation temperature of the eggs. Higher temperatures typically result in the development of female turtles, while lower temperatures result in the development of male turtles.
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