Final answer:
In the absence of linkage, the expected phenotypic ratio in the F2 generation of a dihybrid testcross can be determined by applying the product rule. This means considering the independent assortment and dominance of alleles. For example, in a dihybrid cross, if we ignore one trait and consider only the other, we would expect a 3:1 ratio for that trait. Using this approach, we can calculate the expected phenotypic ratios for the F2 generation.
Step-by-step explanation:
Because of independent assortment and dominance, the 9:3:3:1 dihybrid phenotypic ratio can be collapsed into two 3:1 ratios, characteristic of any monohybrid cross that follows a dominant and recessive pattern. Ignoring seed color and considering only seed texture in the above dihybrid cross, we would expect that three-quarters of the F₂ generation offspring would be round, and one-quarter would be wrinkled.
Similarly, isolating only seed color, we would assume that three-quarters of the F₂ offspring would be yellow and one-quarter would be green. The sorting of alleles for texture and color are independent events, so we can apply the product rule.
Therefore, the proportion of round and yellow F₂ offspring is expected to be (3/4) × (3/4) = 9/16, and the proportion of wrinkled and green offspring is expected to be (1/4) × (1/4) = 1/16.
These proportions are identical to those obtained using a Punnett square. Round, green, and wrinkled, yellow offspring can also be calculated using the product rule, as each of these genotypes includes one dominant and one recessive phenotype.
Therefore, the proportion of each is calculated as (3/4) × (1/4) = 3/16.