Color enhanced light micrograph of fruit fly salivary gland chromosomes. The fruit fly, Drosophila, is one of the most valuable of organisms in biological research, particularly in genetics and developmental biology. Part of the reason scientists use drosophila is historical - so much is already known about it that it is easy to handle and well-understood - and part of it is practical: it's a small animal, with a short life cycle of just two weeks, and is cheap and easy to keep large numbers. Mutant flies, with defects in any of several thousand genes are available, and the entire genome has been sequenced.