The goal of using such models is always to gain a general understanding of biological events that occur in or affect humans. As a result, much is already known about E. coli, and since all genetic material is similar, findings in bacteria have relevance to humans and other higher organisms. Scientists study the fruit fly, Drosophila melanogaster, because it is more complex than E. coli but can still be easily maintained in the laboratory. Fruit flies have easily studied chromosomes and reproduce rapidly, so the effects of genetic changes can be determined relatively quickly. Equally important is the fact that like E. coli, these flies have been studied for many years and a great deal is known about their genetics, biochemistry, and behavior.
Mice are valuable research animals that are genetically much more complicated than flies.
Many mutant strains of mice that have been specially bred for research are available today. Breeders provide investigators using the mice with information on the animals' genetic background, diet, and other characteristics so that variables which might confuse the research results are minimized. Scientists can also select animals that are particularly prone to developing certain tumors, metabolic disorders, or other conditions. Researchers who modify the genes of test animals to produce, for example, especially large mice or red-eyed flies are attempting to learn vital facts about gene expression and control. Knowing how genetic processes are regulated may someday have relevance to a host of human diseases which develop when normal function goes awry.