1994 Woodrow Wilson Biology Institute
Since early in the 1900's, fruit flies (Drosophila) have been used as an organism for studying genetic variation. Their small size, rapid reproductive cycle, and their large number of offspring make them excellent subjects for genetic study. Easily cultured, one female has the potential of producing five hundred eggs in ten days, and phenotypic variations are easily observable using a dissecting microscope. Mutant phenotypes in Drosophila originate by spontaneous mutation and purposeful exposure to radiation or chemicals.
Thomas Hunt Morgan, and other early researchers studying Drosophila at Columbia University, investigated combinations of traits in organized mating of flies. Careful observations of genetic cross results and statistical records were kept which allowed researchers to establish that Drosophila traits are carried on four pairs of chromosomes.
As early as 1913 Alfred Sturtevant recognized that genes carried on the same chromosome pair can be exchanged by the mechanism of crossing over, and that the rate of crossing over is an indication of the distance between genes on the chromosomes. The work of the early Drosophila geneticists confirmed Mendel's basic laws of inheritance.
Drosophila genome consists of 165 million base pairs in contrast to the human's 3,000 million base pairs. The sequencing of the fly's DNA and gene manipulation have aided biologists in perfecting skills in gene manipulation and has given insight into how genes function in living organisms. Techniques in gene analysis and gene manipulation are currently being applied in the Human Genome Project, which has the goal of sequencing the entire human genome by the beginning of the twenty first century,
Through a series of activities and hands-on lab work in this unit, students will gain an understanding of basic genetic principles and current trends in genetic technology. These activities and labs may be used as separate independent exercises, or as a whole unit, based upon individual teacher's needs.
Each lab will provide a description of supplies and procedures. Fruit flies are available from a number of biological supply houses or flies can be collected as described in the lab "Collect Your Own Drosophila." Transparent glass or plastic vials with a volume of 50-100 mL are appropriate as culture vessels. Plugs for vials can be made of foam (polyurethane) or nonabsorbent cotton. Instant Drosophila medium can be inexpensively purchased and mold inhibitor should be included in the Drosophila medium. Plastic inserts can be made or purchased to place in individual culture vials to provide a larger surface area for pupating Drosophila.