He conducted groundbreaking experiments with fruit flies (Drosophila melanogaster) in the early 20th century. His work demonstrated the following:

* Genes are linked: He observed that certain traits were inherited together, suggesting that the genes responsible for these traits were located on the same chromosome.

* Chromosomes exchange genetic material: He discovered the process of crossing over, where homologous chromosomes exchange genetic material during meiosis. This explained how linked genes could sometimes be separated.

* Genes are located on specific chromosomes: Morgan's experiments with fruit flies showed that specific traits could be mapped to specific chromosomes, confirming the location of genes on chromosomes.

His work revolutionized our understanding of heredity and laid the foundation for modern genetics.