Genes were linked / genes on the same chromosome and closely associated.
Detailed Answer :
The F2 ratio deviated from that of Mendel's dihybrid F2 ratio (9 : 3 : 3 : 1) in an experiment performed by Morgan on Drosophila because of Linkage. The genes were linked if they were located on the same chromosome and closely associated, therefore, they failed to segregate at the time of gamete formation resulting in greater number of parental combinations and lesser number of new recombinations in F2 generation thereby deviating from the normal dihybrid Mendelian ratio.
