why do some fruit flies have white eyes

The fruit fly Drosophila melanogaster possesses disproportionately large, oftenбvividly colored eyes. These range in color from red to sepia to white and indicate a great deal about the fly s genetic makeup. Someбfruit flies bred in the wild have red eyes. Brown and sepia eyes are a result of a recessive gene and only occur when two sepia-eyed flies mate. White, vermillion and cinnabar-eyed fruit flies result from mutations and are far less common. Because fruit flies are genetically simple insects and have rapid life cycles, they are ideal subjects for biological study. Particularly in genetic experiments, fruit flies provide researchers with extremely useful information.

Fruit fly phenotypes manifest prominently, resulting in red-, sepia- and white-eyed flies. In rare cases, eyeless flies are produced through genetic experimentation. Other genetic mutations are obvious in male-female ratios and wing shape. While white-eyed fruit flies are genetic anomalies, they are relatively common in science classrooms and laboratories. The white-eyed fruit fly gene is recessive and typically is eliminated after mating with dominant-eyed fruit flies for two generations. White eyed fruit flies that mate with other white-eyed fruit flies will produce white-eyed offspring.
Click on the small thumbnail pictures below to magnify the flies. You'll see enlarged illustrations of fruit flies, Drosophila melanogaster. (In our real exhibit you'd be looking at the actual flies crawling around, looking for food or grooming their wings. ) Compare the mutated flies to the normal flies.

The fruit flies in this exhibit show just a few of the mutations that occur in natural fruit fly populations. The genetic instructions to build a fruit fly-or any other organism-are imprinted in its DNA, a long, threadlike molecule packaged in bundles called chromosomes. Like a phone book made up of different names and addresses, each chromosome consists of many individual sections called genes. Each gene carries some of the instructions for building one particular characteristic of an organism.

To build a complete organism, many genes must work precisely together. A defect in a gene can cause a change in the building plan for one particular body part-or for the entire organism. Mutations are neither good nor bad: some may be beneficial for an organism; others may be lethal. By creating new gene versions, mutations are a driving force for changes in evolution, sometimes leading to new species. Biologists learn about the proper function of any gene by studying mutations. If a defective gene causes short wings, for instance, scientists know that the healthy version of the gene is responsible for correct wing formation.

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