To understand the biology of other organisms, species called as model organisms are used. In the case of genetic investigation, scientists used fruit flies as their model organism since they share 75% of the genes that cause disease with humans. Fruit flies are also great to work in a research setting because they are relatively easy to take care of, especially compared to larger and more expensive organisms like rats or fish. Fruit flies are of low maintenance creatures with regards to their habitat and their food. I hope this answer helps.
