Morgan experimented and found that when the two genes in a hybrid cross situated on same chromosone, the proportion of parental gene combination were much higher than the non-parental type..
Based on this observation, he coined the term recombination.
To describe the generation of non-parental gene combinations
Morgan was the first one to hypothesize the frequency of recombination was related to the disatnce between the genes on a chromosome. However, Sturtevant was the first one to explain that the proportion of the crossover during crossing over could be used as an index of the distance between genes. Based on this, he also constructed the genetic map of fruit flies.