Have you ever noticed the tiny fruit flies flitting around your fruit bowl in the summertime? Did you know that they have been used for genetic research for nearly a hundred years? Genetics is the study of how traits are passed from one generation to the next. The types of living things that work best for genetic studies are easy to keep in a lab, have lots of offspring, and most importantly, have short generations. A generation is an average time between the birth of the parents and the birth of the parents’ offspring. A human generation is twenty-five years or more. A fruit fly generation is two weeks.
The common fruit fly is a model organism for genetic studies. It is so widely used that it is easily cultured in the lab and classrooms, has a short generation time, and can produce many offspring. The life cycle (from egg to adult) takes about ten days at room temperature. Eggs are laid and hatch into first instar larvae. These larvae feed voraciously on the culture medium provided, e.g., ripe banana. You can observe this by looking at a culture bottle - you should see many tunnels in the medium made by tiny white larvae (or maggots). These first instar larvae go through several instar stages, and eventually, the third instar larvae crawl up the sides of the bottle away from the culture medium. There they stop, and their larval cuticle hardens, forming a dark brown pupa. Metamorphosis takes place during the pupae stage. Larvae tissues degenerate and reorganize, creating an adult fly inside the pupae case. When metamorphosis is complete, the adult fly emerges from the pupae case. After the fly emerges, the wings expand and dry, the abdomen becomes more rotund, and the color of the body darkens.
Sexing Drosophila The female abdomen has seven segments, several dark transverse stripes, and is pointed at the tip. The abdomen of the male has only five segments, two dark stripes, and a more rounded, heavily pigmented tip. In immature males, pigmentation may not be developed. Fruit flies have other characteristics helpful for research. Fruit flies have many genetically derived traits, like red, white, and brown eye color, that are easy to identify. It is also helpful for research that it’s relatively easy to tell the sexes apart. Male fruit flies are smaller, and their abdomens are less pointy than females’ abdomens, with a distinctive black patch.
Procedure Peel the banana and place it in an uncapped jar outside.
In a couple of hours, you should find tiny fruit flies crawling around the banana. It would help if you captured several fruit flies for this experiment to work. If no fruit flies have arrived on your banana, try waiting a couple more hours.
Cover the jar with stockings and secure it with a rubber band.
Using the magnifying glass, try to observe fruit flies and see if you can identify the males and females.
Using small paintbrushes like watercolor brush, get a pair of male and female fruit flies. Put them in a separate jar. Take note of the characteristics of the wings, eye color, antenna, and sex.