Drosophila melanogaster, a common fruit fly, was one of the first model organisms used in genetic research, and continues to be one of the most important. Thomas Hunt Morgan (1866-1945) developed Drosophila as a model system in 1909. Morgan, along with his students, Calvin Bridges, Alfred Sturtevant, and Hermann Muller, made some of the most important discoveries in genetics through their work with Drosophila. Among these were the genetic explanation of sex linkage (the location of a gene on a sex chromosome); proof that genes are contained on chromosomes; and the demonstration that genes are arranged on a chromosome in a linear order with fixed, measurable distances between them, the principle that underlies genetic mapping.

Like other good model organisms, Drosophila is easy to rear in the laboratory. It has a short life cycle, lasting about two weeks, and produces many offspring. Each female can...