The phenomenon which defies the independent assortment is
Mendel conducted dihybrid cross and postulated third law of inheritance. When a cross is made between two individuals different from each other in two or more characters, then the inheritance of one character is independent of the inheritance of another character. It is called Law of independent assortment. But Linkage is exception to law of independent assortment, because, the genes present on the same chromosome may or may not show independent assortment and are inherit together. It is called Linkage.
So, the correct option is ‘Linkage’.