Model organisms: The fruit fly

29/8/02. By Richard Twyman

The fruit fly Drosophila melanogaster has the longest history of any model organism and has been widely used to study genetics and developmental biology.

The fruit fly (Drosophila melanogaster) is a small insect that feeds and breeds on spoiled fruit. It has been used as a model organism for over 100 years and thousands of scientists around the world work on it. Part of the reason for this is historical. Scientists today choose to study the fruit fly because so many others have done so before them. There are established methods for handling flies in the laboratory and an immense volume of data has accumulated about fly biology. But why was the fruit fly chosen in the first place?

As with most of the long-established model organisms, the initial choice was for practical reasons. The fruit fly is small and has a simple diet. Therefore, large numbers of flies can be maintained inexpensively in the laboratory. The life cycle is also very short, taking about two weeks, so large-scale crosses can be set up and followed through several generations in a matter of months. Fruit flies also have large polytene chromosomes, whose barcode patterns of light and dark bands allow genes to be mapped accurately.

Due to these advantages, fruit flies were extensively used in the early 20th century to work out the principles of genetics. Indeed, they are still used in this capacity to teach genetics in schools. Mutants are available for a large number of genes and new mutations can be induced very easily by exposing flies to radiation or adding mutagenic chemicals to their food. This ability to recover mutants means that flies can be used to investigate the genetic basis of any conceivable biological process.

The fruit fly (Drosophila melanogaster) has been used as a model organism for nearly a century.

The relevance of the fruit fly to the human genome project reflects the remarkable conservation among genes in different animals. The fly genome, which was sequenced in the year 2001, is 165 million base pairs in length (spread over four chromosomes) and contains approximately 14 000 genes.

The human genome contains 3-4 times as many genes but most of these are thought to have arisen by two rounds of genome doubling during the evolution of vertebrates. Therefore, humans have more genes than flies but about the same number of gene families. Since it is easy to create mutants and carry out experiments on fruit flies, the functions of many fly genes have been established.

The relationship between fly and human genes is so close that the sequences of newly discovered human genes, including disease genes, can often be matched against their fly counterparts. This provides a lead towards the function of the human gene and could help in the development of effective drugs.

The analysis of fly embryonic development has made a particularly important contribution to the understanding of developmental processes in humans. The genetic basis of many human birth defects is now known thanks to experiments on developmental mutants in the fly.

In acknowledgement of this, Ed Lewis, Christiane Nusslein-Volhard and Eric Wieschaus, who led early work on Drosophila developmental genetics, were awarded the Nobel Prize in Physiology or Medicine in 1995.

Further reading

Feature: Why the fly?

The Nobel Prize in Physiology or Medicine 1995

Adams MD et al. The genome sequence of Drosophila melanogaster. Science 2000 Mar 24;287(5461):2185-95. Abstract

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