Answer:
He discovered that certain traits were linked to the X chromosome.
Step-by-step explanation:
Morgan's research led him to formulate the chromosomal theory of heredity and won him the Nobel Prize in Medicine in 1933.
At Columbia, Morgan began to study heredity with a team of students, experimenting with Drosophila ampelophila and Drosophila melanogaster, which proved Mendel's theories and enabled the principles of genetics to be determined. Morgan proved the reality of genes as bodily elements of specific location on chromosomes.
In addition, his major contribution to science was the discovery that certain characteristics were linked to the X chromosome, which made possible the formulation of the concept of inheritance linked to sex.