What information did Thomas Morgan provide regarding the chromosomal theory of inheritance?

(N/A) Thomas Hunt Morgan and his colleagues provided the experimental verification of the chromosomal theory of inheritance.
They laid the foundation for understanding the variations observed in sexually reproducing organisms.
Morgan worked with the fruit fly,$Drosophila$ $melanogaster$. He chose this organism because:
$1$. They could be grown on simple synthetic media in the laboratory.
$2$. They complete their life cycle in about two weeks.
$3$. $A$ single mating could produce a large number of progeny flies.
$4$. There was a clear differentiation of the sexes; the male and female flies are easily distinguishable.
$5$. It has many types of hereditary variations that can be seen with low-power microscopes.