How many phenotypic classes are expected when two homozygous dominant and two heterozygous parents are crossed for two traits?

To determine the number of phenotypic classes expected when crossing two homozygous dominant parents with two heterozygous parents for two traits, it's essential to understand the concepts of genotype, phenotype, and how traits assort during a dihybrid cross.

When two traits are involved, each trait can exhibit dominance or recessiveness. In this scenario, the homozygous dominant parents can only contribute one type of allele for each trait, while the heterozygous parents contribute two types of alleles. This combination leads to a variety of genotypes.

For two traits, you can use a Punnett square or the principles of independent assortment to visualize the possible combinations. Each trait can yield different combinations of dominant and recessive phenotypes. If the homozygous dominant parents are homozygous for both traits (let's say AA and BB for Trait 1 and Trait 2), and the heterozygous parents are heterozygous (AaBb), the crosses might yield:

1. Homozygous dominant for both traits (AABB)

2. Homozygous dominant for one trait and heterozygous for the other (AABb, AaBB)

3. Heterozygous for both traits (AaBb