Like most college students, I crave sweets, especially during times of stress, which during this overcommitted sophomore year means most of the time. I love glazed doughnuts and SweeTarts, vanilla ice cream with hot fudge and sprinkles. I love the juice of a perfectly ripe peach as it drips down my chin. I must get to that peach fast, though, or I’ll have to fight the one whose love of sweet things gives it its name: Drosophila melanogas?ter, more commonly known as the fruit fly, because it feeds on decaying fruit.
My biology professor, Kenneth Miller, used Drosophila to introduce a lecture on linked genes last February. A nuisance at picnics, Drosophila is invaluable to the study of genetics. Thomas Hunt Morgan pioneered the use of D. melanogaster as the “model organism.” He practiced experimental evolution, the precursor to population genetics, and he studied how heredity influences evolution following patterns of Mendelian inheritance. Wild-type fruit flies have gray bodies and normal wings, but Morgan found flies with black bodies and vestigial wings—both of which are recessive traits. This discovery and his ensuing experiments led to an understanding of gene linkage, genetic recombination, and the use of gene mapping. D. melanogaster is also extraordinarily easy to cultivate and keep. The flies have only four pairs of chromosomes and a life cycle of approximately two weeks. They are small (about three millimeters in length), fecund, and fertile year-round; they have a short generation time and are cheap to keep in large numbers. These factors make them attractive test subjects, and their large populations make statistical analysis simple and reliable.
As I read about the insects for my biology classes (you’ll find Drosophila in any biology textbook), I learned that, despite their relatively small number of chromosomes, they exhibit some distinct and complicated behaviors, such as sperm competition. Males of this polygynous species eliminate rival sperm with toxic substances in their seminal fluid. Think about that the next time you choose a boyfriend. Is he in it for love or personal gain?
Flies are currently available for purchase, as long as you have a major credit card. They are U.S. Department of Agriculture–approved. Mutants cost no extra. Eugenics is not frowned upon. In fact it is encouraged: name your phenotype and the vendor will name the price.
However, one unseasonably warm Saturday last October, I needed no credit card to attract fruit flies. As I lay on the College Green soaking up the sun and reading about modern European women’s history, my bare feet were enough. A fly landed on my right big toe, first exploring the few blonde hairs at the joint, then slowly moving toward the nail. It parked itself there and waited. It was large and had a gray body (with black markings) and normal wings: a wild-type. Its red eyes encompassed most of its head.
Had I captured the fly and brought it back to the laboratory, we could have mated it with a recessive white-eyed fly, or a black-bodied Drosophila with vestigial wings, then examined the first and second filial generations for the same mutations. Eye color is an X-linked gene. Body color and wing shape are linked genes. I could have created a gene map and plotted recombination frequencies to determine distance between genes on the chromosomes by analyzing the phenotypes in each generation.
Instead, I was content to let the fly explore the ridges of my feet. When I have a child and she demonstrates her love of sweet things, I will beckon her and remember my encounter with the fruit fly: “Come here, my little Drosophila,” I’ll say. “I love you.”
Vaughn Edelson, from Miami, is concentrating in human biology.
