A Summer in the Fly Lab
1Rohan Bergstrom spent his summer helping in Dr. Ifeoma Bassey's genetics lab at the community college. The lab raises fruit flies in plastic vials with a layer of food at the bottom. Fruit flies are useful for studying genes because they are small, easy to feed and produce a new generation in about two weeks.
2Dr. Bassey explained that a gene is a section of DNA that carries the instructions for building a protein. Proteins do much of the work in a body: some give color, some build structures such as wings and some break down chemicals. A mutation is a change in the DNA of a gene. Because a protein's shape decides what it can do, a mutation that changes the protein's shape can change how well that protein works.
3The lab keeps five strains of flies. Each mutant strain differs from the normal strain by one known mutation. In strain W, the eye-color gene is changed and the red pigment protein is not made. In strain V, the wing gene is changed and the wing protein is misshapen. In strain N, a gene is changed, but tests show the protein it builds has the same shape as the normal protein. In strain R, the gene for a protein that breaks down a pesticide is changed, and the protein works faster than normal.
4Rohan ran two tests with 100 adult flies from each strain. In the pesticide test, flies spent 24 hours in a cage with a low dose of pesticide, and he counted the survivors. In the shelf test, flies were released at the bottom of a tall clear box with food on a high shelf, and he counted how many reached the food within one hour. Dr. Bassey told him that differences of 3 percentage points or less are within the normal spread between repeated trials, so they do not count as a real difference.
5In ordinary vials, with food at the bottom and no pesticide, flies of all five strains lived about the same length of time, roughly 40 to 50 days. Rohan recorded each test result in the table below. He also noted that the lab keeps every strain in its own labeled vials, so flies from different strains do not mate and mix their mutations.