## The biggest celebrity among genetic model organisms is the fruit fly Drosophila melanogaster

When Thomas Morgan (1866 – 1945) first saw the white-eyed male fly Drosophila melanogaster in his laboratory at Columbia University in New York, he had no idea that he was at the beginning of a discovery that would bring him the Nobel Prize 20 years later. Indeed, an experiment in which he crossed white-eyed mutant flies with standard red-eyed partners that led to the discovery that the genes are located on chromosomes (Figure 20.5).

Thanks to Morgan and his students at Columbia University in New York, Drosophila became the "main figure" for the study of genetic control of biological processes in animals. Its short life cycle (up to 14 days), easy breeding and wide repertoire of techniques that allow for sophisticated genome manipulations are some of the attributes that have made Drosophila probably the most widely used model organism.

After Morgan laid the foundation for the chromosome theory of inheritance, several hundred mutants were prepared that showed various developmental disorders either in the larval stage or in adult flies. Examples of such mutants are Ultrabithorax, which produces one extra winged limb; Antennapedia, which has an extra pair of legs instead of antennae; or eyeless (ey), lacking eyes. Remarkably, when the genes whose alteration leads to developmental disorders in mutants were identified, similar genes were found to occur in the human genome. And not only that, the products of these genes are also involved in the correct course of ontogenesis. And just as Paul Nurse showed in yeast, mammalian and Drosophila genes were found to be interchangeable. That is, when the human gene was inserted into the genome of the Drosophila mutant, its proper ontogeny was restored. Conversely, Drosophila genes worked well in mammals. The fact that the ey gene is involved in the formation of the eye was proven by the fact that when it was artificially activated in different parts of the body of Drosophila (for example, on the legs), the formation of eyes took place in them. When such (so-called ectopic) expression was done with the mouse gene Pax6, which is similar to ey, the result was the same (eye formation in "inappropriate" body parts). The results of these fascinating experiments confirmed that the ontogeny processes of Drosophila and mammals are under similar genetic control, so the results obtained in these small dipterans are also relevant for animals like us.