, T.H. Morgan observed in Drosophila that when two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations was much higher than the non-parental (recombinant) type. He attributed this to the physical association or linkage of the two genes on the same chromosome . If the genes were on different chromosomes, they would assort independently, resulting in equal proportions of parental and recombinant offspring.