Fruit flies

Fruit flies were used to study genetic inheritance, leading to the discovery of linked and independent inheritance. Fruit flies have only four chromosomes pairs in each cell, are simple to feed, and breed often. Using them in research greatly hastened the pace at which knowledge of genetic mechanisms increased.
 Thomas Hunt Morgan United States 1907 Fruit flies

Fruit flies were used to study genetic inheritance, leading to the discovery of linked and independent inheritance. Fruit flies have only four chromosomes pairs in each cell, are simple to feed, and breed often. Using them in research greatly hastened the pace at which knowledge of genetic mechanisms increased.