What ratio of phenotypes is expected when two organisms heterozygous for two traits are crossed?

When two organisms that are heterozygous for two traits are crossed, they exhibit a dihybrid cross. In a dihybrid cross, each organism can produce gametes that contain combinations of the two traits. For example, if we denote the two traits as A (dominant) and a (recessive) for the first trait, and B (dominant) and b (recessive) for the second trait, the genotypes of the parents would be AaBb for both.

When combining these traits, the possible gametes produced by each parent are AB, Ab, aB, and ab, resulting in a 4x4 Punnett square. When the combinations are analyzed, the resulting phenotypic ratio for two traits will typically follow Mendel's law of independent assortment, which predicts a 9:3:3:1 ratio.

This means that out of 16 possible offspring, 9 will show both dominant traits, 3 will show the first dominant trait and the second recessive trait, another 3 will show the first recessive trait and the second dominant trait, and 1 will show both recessive traits. Therefore, the expected ratio of phenotypes is 9:3: