Tom Turpin
Professor of
Purdue University







Fruit Flies Have Great Genes

What has 10 wheels and flies? Before you start calculating the number of wheels on your favorite airplane, think insects. The answer to that old grammar school joke is: a garbage truck. Most of us recognize the implication of the joke that, at least in warm weather, garbage and flies are inseparable.

Some of those flies hanging around the garbage might just be a group of flies known as Drosophilia, the fruit flies. These little flies, only 3 to 4 millimeters in length, are named for the fact that they live on decaying fruit. There are many kinds of fruit flies, and they are very common insects. So common that it is nearly impossible to have ripe fruit lying around for any length of time without attracting a few of the little creatures.

While fruit flies are a nuisance to most of us, biologists have made good use of one species, Drosophila melanagaster. For many years, fruit flies have been the standard animal used in genetics research and teaching. The flies are easy to grow, reproduce rapidly and have big chromosomes.

Scientists over the years have developed many strains of this fruit fly, all which have different physical characteristics. Some of these strains can be purchased through biological supply houses for use in teaching genetics in biology.

Several eye colors exist. Regular old fruit flies, those that show up around the overripe banana on your kitchen counter, have red eyes. You can get flies with clear ruby eyes, or vermilion or white or apricot or brown. You can even get a strain of fly that has red eyes that dull with age.

Normally the fruit fly holds its wings along the back when it is at rest. But scientists have produced a strain that holds its wings at right angles to the body. You can get a fly with almost no wings, called vestigial winged, or one with no wings all. Some have wings that curl upward. On another strain the wings are truncated.

If you don't like the normal yellowish color, you can buy a fruit fly that is black. Or you can get one with forked bristles on its body; normal ones have straight bristles.

All of this makes for some interesting combinations and descriptions of fruit flies. For instance, you can buy a strain of fly that has white eyes, miniature wings and forked bristles. Or you can get one that has curly wings and plum eyes with divergent wings and short-and-thick bristles. Now I'm not sure what you get if you cross a forked-bristle fly with a short-and-thick-bristle fly. It would make a good experiment in a science classroom, and that is how these insects are used.

For most of us, the only fruit flies we are interested in are those that are sold as the wild type — described as normal characteristics with a red eye color. Those are the ones we find in our kitchens. In general, the description we most appreciate is one that goes like this: small blob of yellow insect smashed on countertop!


Writer: Tom Turpin
Editor: Andrea McCann