The hereditary principle derived from the results showing new combinations in addition to parental combinations in F2 generation is
Law of independent assortment
In the dihybrid cross, the phenotypes round, yellow; wrinkled, yellow; round, green and wrinkled, green appeared in the ratio 9:3:3:1. Such a ratio was observed for several pairs of characters that Mendel studied. In Mendel’s dihybrid cross along with parental combinations, recombinants are also obtained. As the genes controlling these two characters are present on separate chromosomes, they get separated during gamete formation which results in recombinations. Based upon such observations on dihybrid crosses (crosses between plants differing in two traits) Mendel proposed a second set of generalisations that we call Mendel’s Law of Independent Assortment. The law states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters.