What principle does a dihybrid cross express?

A dihybrid cross expresses the principle of independent assortment, which states that the alleles for different traits segregate independently of one another during gamete formation. This principle was first demonstrated by Gregor Mendel through his experiments with pea plants, where he studied the inheritance of two traits simultaneously. The resulting phenotypic ratio in the offspring is typically 9:3:3:1 for two traits that are assorting independently.