Drosophila melanogaster is only about 3 mm long, but like C. elegans, it is a giant in the biology lab. The flies are easy to rear in plugged jars containing rotting fruit or a mix of water, yeast, sugar, cornmeal, and agar. The fruit fly’s genome sequence was completed in 1999; many of its 13,600 genes have counterparts in humans. But these relatively recent findings belie Drosophila’s century-long history as a model organism. This list includes some of the most important research areas:
In the early 1900s, Thomas Hunt Morgan and his colleagues used Drosophila to show that chromosomes carry the information of heredity. Studies on mutant flies with different colored eyes led to the discovery of sex-linked traits. Morgan’s group also demonstrated that genes located on the same chromosome are often inherited together. In the process, they discovered crossing over, linked genes, and sex linkage.
The similarity of some Drosophila genes to those in the human genome has led to important insights into muscular dystrophy, cancer, and many other diseases. For example, researchers have studied the fly version of the human p53 gene, which induces damaged cells to commit suicide (apoptosis). When that gene is faulty, the cell may continue to divide uncontrollably. The result: cancer.
Homeotic genes are “master switch” genes that regulate the overall development of the body, including segmentation and wing placement. Researchers discovered these genes in mutant flies with dramatic abnormalities, such as legs growing in place of antennae on the fly’s head. Later, researchers discovered comparable genes in many organisms, including mice, leading to new insights into mammalian development.
The expression of some genes in bacteria, plants, fungi, and animals cycles throughout a 24-hour day. How do the rhythmically expressed genes “know” what time it is? In Drosophila, clock genes called period and timeless encode proteins that turn off their own expression, much as a thermostat turns off a heater when the temperature is too high. This “master clock” controls the animal’s other daily cycles of hormone secretion and behavior.