You're asking about a very broad question! There are thousands of genes in fruit flies, and it's impossible to know which specific gene you're referring to without more information.

To help me answer your question, please tell me:

* What is the full name or symbol of the gene? (e.g., "G" isn't enough - it needs to be something like "G6PD" or "white").

* What kind of trait or function are you interested in? (e.g., eye color, development, behavior, etc.)

Once I have this information, I can tell you what gene "G" is responsible for in fruit flies.