In a dihybrid cross, what does the phenotypic ratio 9:3:3:1 represent?

In a dihybrid cross, the phenotypic ratio of 9:3:3:1 represents the distinct combinations of traits resulting from the combination of two different genes, each with two alleles. This ratio emerges from a genetic cross where both parents are heterozygous for two traits, allowing for the expression of different phenotypes in the offspring.

Specifically, in the 9:3:3:1 ratio, the "9" corresponds to individuals expressing both dominant traits, "3" represents those having one dominant and one recessive trait for the first gene while being dominant for the second, the second "3" indicates individuals expressing the opposite combination (dominant for the first trait and recessive for the second), and the "1" denotes those that express both recessive traits. This variety in phenotypes is due to the independent assortment of gene pairs during gamete formation, a fundamental concept observed during Mendel's experiments with pea plants.

Thus, the correct answer accurately captures the essence of the genetic diversity that arises from a dihybrid cross, illustrating how multiple traits can assort independently to produce a range of phenotypic outcomes.