When the two homozygous parents differing in two pairs of contrasting traits are crossed, the inheritance of one pair is independent of the other. In other words, when a dihybrid forms gametes, assortment (distribution) of alleles of different traits is independent of their original combinations in the parents.
Many genes are located on one chromosome, i.e. they are linked. Therefore, they pass through gametes in the form of a linkage group. However, recombinations are due to the crossing over that takes place during meiosis.
Therefore, the law of independent assortment is applicable only for the traits which are located on different chromosomes. Thus, law of independent assortment is not universally applicable.