Final answer:
The expected phenotypic ratio from a dihybrid cross showing independent assortment is 9:3:3:1, arising from the independent assortment of two heterozygous traits, each with one dominant and one recessive allele.
Step-by-step explanation:
The phenotypic ratio resulting from a dihybrid cross showing independent assortment is expected to be 9:3:3:1. This ratio emerges from the mating of individuals that are heterozygous for two traits, assuming that each gene has two alleles with one being dominant and the other recessive, and that the genes sort independently into gametes.
This 9:3:3:1 ratio can also be understood by looking at each trait separately, following the principle of independent assortment articulated by Gregor Mendel. For instance, considering two traits such as seed shape and color, if we cross two plants heterozygous for both traits (RrYy), the outcome can be predicted by using a Punnett square or the probability method. The resulting proportion for the dominant phenotypes is calculated as (3/4) × (3/4) = 9/16 for plants exhibiting both dominant traits. Other phenotypic proportions (3/16 and 1/16) can be calculated similarly, explaining the complete 9:3:3:1 distribution.