Two-winged guinea pig

From early summer to the first frost, innumerable small flies or gnats called fruit or vinegar flies plague our dining tables, picnic spreads, fruit bowls, and trash containers. These tiny flies are only about 1/16th of an inch in length, and can easily wriggle through the meshes of ordinary screening and infest our homes or other places where food is stored. Though this pestiferous fly may be quite annoying on occasion, there is little evidence that it routinely transmits pathogenic microbes to our food as does its infamous cousin, the housefly.

Drosophila is the scientific name of this group of insects, and hundreds of different species are distributed worldwide. Mankind is greatly indebted to this minuscule fly as it has been the “guinea pig” for more scientific research than any other creature, with the possible exception of man.

Early in the 20th century, the science of genetics was born with the rediscovery of the work of the Austrian monk Gregor Mendel, who had reported on the basic laws of inheritance some 35 years earlier. Mendel had used the common garden pea in his experiments, but considerable time was required after a cross was made before the results could be observed.

Dr. Thomas Hunt Morgan, a zoology professor at Columbia University, quickly saw the importance of Mendel’s work and around 1905 decided to expand it. Thus began a fruitful line of investigation into the mystery of how characteristics of living things are passed from one generation to the next—the secret of life itself.

Largely by accident, Morgan stumbled onto the fruit fly while searching for an experimental animal that would be suitable for his purposes. Drosophila was ideal in that it was easy to rear in large numbers in a limited space and, under controlled conditions, a new generation could be produced in 10 to 14 days. The flies were raised in cotton-plugged pint milk bottles to which a mixture of bananas and yeast had been added as food for the developing maggots.

Shortly after Morgan’s success with the fruit fly as an ideal experimental animal, most other genetic research centers adopted it for their work. The University of Texas became a leading research center for Drosophila genetics (forgive me for plugging my alma mater), and when I was a student there, two full-time technicians were employed to wash, autoclave, and prepare hundreds of milk bottles for the rearing of the flies.

The names of Morgan and Drosophila, however, will always be inseparably linked. Aided by a group of brilliant graduate students (Calvin Bridges, Herman J. Muller, and Arthur Sturtevant), the enigma of how sex was determined in an individual was solved as was the mystery of sex-linked inheritance (color blindness and hemophilia are two sex-linked traits in humans). In their laboratory at Columbia, affectionately known to their colleagues as “The Fly Room,” they discovered that the gene-bearing chromosomes routinely exchanged parts when the reproductive cells divided, and this led to the first mapping of the location of the units of inheritance on the individual chromosomes. For his definitive work in genetics, Morgan was awarded the Nobel Prize in 1934. H.J. Muller, one of the celebrated students, later won a Nobel Prize when he demonstrated that changes or mutations in the genetic material of the fruit fly could be artificially induced by bombarding them with X-rays, thus founding the science of radiation genetics.

Over the years, other primitive organisms have been used to investigate the secrecy of the gene. Important discoveries have been made using the red bread mold, Neurospoa, and a common bacterium, Esherichia coli, found in everyone’s intestinal tract. The behavior of the genetic material of these primitive forms has been proven to be identical with that of plants and animals, including man.

Try think kindly toward the fruit fly the next time a swarm of them annoy you. Remember, not too many other species are as famous as this tiny fly.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

From the Aug. 31-Sept. 6, 2005, issue

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