A dihybrid cross involves two pairs of contrasting characters, eg, yellow round seeded plant and wrinkled green seeded plant (both pure lines) homozygous. When a dihybrid cross is made between two pure line of homozygous parents, then the F, generation shows hybrids with dominant phenotypic effect. When F1 heterozygous plants are self-fertilized to produce F2 generation, 4 types of combinations are obtained of which two are similar to parental combination and other two are new combinations. The phenotypic dihybrid ratio of these 4 combinations in F2 generation comes out to be 9:3:3:1, while the genotypic dihybrid ratio is 1:2:2:4:1:2:1:2:1.