Final answer:
Environmental factors affecting gene expression are the likely cause of a genetically male breaded dragon developing into a female when exposed to higher temperatures, which override genetic sex determination mechanisms.
Step-by-step explanation:
The likely cause of the phenomenon where a fertilized egg of a genetically male breaded dragon can develop into a female under high temperature is environmental factors affecting gene expression.
In the case of temperature-dependent sex determination, the environment, specifically the temperature, influences whether the expression of genes leads to the development of male or female sex organs. This process is different from the one controlled by the SRY gene on the Y chromosome typical to genetic sex differentiation in humans, where the presence or absence of this gene dictates the sexual development as male or female.
For reptiles like breaded dragons, the phenomenon is an example of environmental sex determination, where the external temperature during the incubation period can override genetic factors. This strategy is seen in several reptiles, including alligators and some turtles, and helps these species regulate their population's sex ratio according to environmental conditions.