Which of the following LED Thomas Hunt Morgan to conclude that crossing over occurs

Question

Which of the following leg Thomas Hunt Morgan to conclude that crossing over occurs

Answer 1

You have not included the choices, however, I do know that TH Morgan was working with fruitflies(Drosophila melanogaster) When he crossed flies with certain traits in each parent and observed the progeny with traits from both parents in the same fly,he proposed the theory of recombination and crossing over in homologues of same pair of chromosomes. Please  include the choices and let me know if you are looking  for crossing over in fruite flies or else. Accordingly, I can post with a diagram.

 

Best,