(A) Monohybrid Cross : Monohybrid crosses are those that involve one pair of contrasting traits. In monohybrid crosses, the phenotypic ratio of the F2 generation is typically 3:1 (III). (B) Dihybrid Cross : Dihybrid crosses are those that involve two pairs of contrasting traits. In dihybrid crosses, the phenotypic ratio of the F2 generation is typically 9:3:3:1 (IV). (C) Incomplete Dominance : Incomplete dominance is when neither allele for a specific trait is dominant over the other. As a result, the phenotype of the heterozygote is somewhere in between the two homozygotes. The phenotypic ratio in such a case is typically 1:2:1 (II). (D) Test Cross : A test cross involves crossing an individual exhibiting the dominant phenotype (but unknown genotype) with a homozygous recessive individual. The phenotypic ratio can be 1:1 (I) if the dominant individual was a heterozygote. If the dominant individual was a homozygote, all offspring will exhibit the dominant phenotype.