Law of independent assortment is based on dihybrid experiment. According to this law, the genes for each pair of characters separate independently from those of other characters during gamete formation.
Example: Consider a plant with yellow round seeds being crossed with another pea plant with green wrinkled seeds. During gamete formation of a dihybrid cross, the factors for yellow colour assort out independently of the factors for round shape. The gene Y may combine with the dominant gene R or the recessive gene r of the other character and enter a gamete. In the same way, the gene y may combine with the dominant gene R or the recessive gene r and enter a gamete. So the F1 dihybrid plants produce four types of gametes and they are YR, Yr, yR and yr. So new combinations not found in the parents could be found in the offspring.