Final answer:
The experiment with fruit flies raised at different temperatures demonstrates how environmental factors influence gene expression, resulting in different phenotypic outcomes such as the number of eye facets.
Step-by-step explanation:
The experiment with three populations of genetically identical fruit flies raised at different temperatures (18°C, 23°C, or 39°C), which resulted in different numbers of facets in the adult compound eyes (950, 840, and 775 respectively), is an example of how environmental factors can influence gene expression. Even though all the fruit flies have the same genetic makeup, the expression of certain genes varies under different conditions, leading to phenotypic differences such as the number of eye facets in response to the temperature at which they were raised. This demonstrates that the expression of genes for cold conditions may differ from those for warm conditions, impacting an organism's phenotype. These differences could have implications for fitness and survival in varying environments. The principle that the environment plays a crucial role in determining gene expression and resulting phenotypes is key to understanding evolutionary processes and adaptations.