Morgan carried out dilybird crosses in drosophila to study genes that showed sex linkage. He hybridised yellow-bodied white eyed females to brown red eyes and carried out the study to `F_(2)` and noticed that the `F_(2)` phenotype ratio deviated from the `9:3:3:1` Mendel dihybrid `F_(2)` phonotypic ratio. Morgan used the genes that were both located on x-chromosome and summed up that the proportion of parental gene combinations is much higher than the non-parental one in case of physical association of genes or linkage of two genes.
