The principle or law of independent assortment can be studied by means of dihybrid cross, e.g., between pure breeding pea plants having yellow round seeds(AABB) and pure breeding having green wrinkled seeds(aabb). The plants of the F1 generation have all yellow and round seeds (AaBb) because yellow and round traits are respectively dominant over green and wrinkled traits. On self breeding, the resultant second filial or F2 generation shows four types of plants. The data obtained by Mendel are as follows:
Yellow and Round=315/556=3/16
Yellow and Wrinkled= 101/556=3/16
Green and Round=32/556=1/16
Thus, the phenotypic ratio of a dihybrid cross is 9:3:3:1.