Linkage will not result in variations among siblings. Morgan carried out several dihybrid crosses in Drosophila to study genes that were sex linked. Morgan came to know that the sex-linked genes were located on the X-chromosome and also observed that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type. It indicates that due to the physical association of the two genes. There will be no variations among siblings.