The genomes of particular nonhuman organisms such as Drosophila have been studied for a number of reasons including the need to improve sequencing and analysis techniques. These nonhuman genomes also provide powerful sets of data against which to compare the human genome.
The fruit fly's genes are similar to those of people. Of the (3382) genes known to cause human disease in mutated form (as of Feb 2012), 75% have been found to have counterparts in the fly. Fathoming fly genes is therefore a step toward knowledge and, hopefully, the treatment of human genetic diseases.
The Drosophila genome has 185 million base pairs and is estimated to have 13,061 genes. The nucleotide sequence of nearly the entire ~ 120-megabase euchromatic portion of the Drosophila genome has been determined. The Drosophila genome was found to encode ~13,600 genes, somewhat fewer than the smaller genome of the roundworm Caenorhabditis elegans, but with comparable functional diversity.
By "Drosophila" here is meant D. melanogaster, long a favorite experimental organism for geneticists. Thomas Hunt Morgan of Columbia University chose it in 1910 as the animal with which he and his students (and their intellectual offspring) would work and come to understand many of the basic principles of genetics.