In any dihybrid cross where both parents are heterozygous for both traits (for example, AaBb x AaBb), the phenotypic ratio of the offspring is typically 9:3:3:1. This ratio results from the independent assortment of alleles, where:
- 9 offspring show both dominant traits,
- 3 offspring show the dominant phenotype for the first trait and recessive phenotype for the second,
- 3 offspring show the recessive phenotype for the first trait and dominant phenotype for the second, and
- 1 offspring shows the recessive phenotype for both traits.
This ratio assumes that the genes are unlinked and assort independently, and there are no interactions between the genes that would alter the phenotypes.
