Linked from
The 29 pages that link to Drosophila melanogaster, each with the reason it gives.
Hox genesRelated: Its Hox mutations made transformations of segment identity experimentally visible.
GastrulationRelated: Its gastrulation shows how coordinated tissue folding creates internal layers.
DiploidRelated: Its somatic cells illustrate diploidy with four chromosome pairs.
Hermann Joseph MullerRelated: Muller used fruit flies to detect mutations across generations.