Drosophila melanogaster

Throughout the last century, the fruit fly Drosophila melanogaster, has been the workhorse for genetic studies in eukaryotes. These studies provided the basis of much of scientists' understanding of fundamental aspects of eukaryotic genetics. Cloned fruit fly genes have led to the identification of mammalian cognates. Discoveries have shown that the conservation between the fruit fly and mammals is much greater than ever expected, from structure proteins to the higher order processes such as development, behavior, sleep, and other physiological responses.

Drosophila melanogaster, is a tiny fly, only 0.08–0.12 in (2–3 mm) in length and is often found around grapes and rotten bananas. They reproduce frequently, furnishing a new generation in less than two weeks; each generation includes hundreds of offspring. They are easy and inexpensive to maintain and easy to examine. Stable mutants will appear after a period of culture in the laboratory. All these characteristics make the fruit fly an ideal model for genetic studies.

In 1903, T. H. Morgan started his work on heredity and chromosomes using the fruit fly. In 1910, Morgan published his famous paper "Sex Limited Inheritance in Drosophila" in the journal Science that described a white-eyed male fruit fly mutant he observed and the crossing experiments he conducted in his laboratory. The research of Morgan and his associates demonstrated that genes for specific traits were located on separate chromosomes. Genes were arranged in a linear order and the relative distance of genes could be determined experimentally. These studies in the first third of the twentieth century established the chromosome theory. Morgan was awarded the Nobel Prize in 1933 for his discoveries on the research of the fruit fly.

The larval stage salivary gland chromosomes of the fruit fly are called polytene chromosomes. They are unique morphologically. The size and length of the chromosomes are greatly increased due to numerous rounds Fruit fly (Drosophila melanogaster) resting on a piece of ripe fruit. Photograph by Oliver Meckes. Photo Researchers, Inc. Reproduced by permission.

of replication. This can be seen easily under the microscope. In 1934, T. S. Painter of the University of Texas published the first drawing of the fruit fly polytene chromosomes, which included the chromosomal localization of several genes. In 1935 and 1938, C. B. Bridges published the fruit fly polytene maps. His maps were so accurate that they are still used even today. These are the pioneer work on physical gene mapping.

The fruit fly genome sequence is the second and the largest animal genome sequenced. The fruit fly has four pairs of chromosomes. The whole genome is about 180 million base pairs. There are about 14,000 genes in the genome. Since the release of an initial draft sequence in 2000, scientists at the Berkeley Drosophila Genome Project (BDGP)and Celera (a private genomic company) continue to release improved versions of the Drosophila genome sequence. The latest version, (Release 3) was released in July 2002.

The conservation of biological processes from flies to mammals extends the influence of the fruit fly research to human health. When an uncharacterized fruit fly homologue of important human gene is isolated, the genetic techniques in the fruit fly system can be applied to its characterization. The identified fruit fly cognates of the human disease genes will also greatly expedite the progress of human disease research.