What does a 9:3:3:1 ratio indicate when crossing two dihybrids?

A 9:3:3:1 ratio in the offspring of a dihybrid cross indicates that the two traits being considered assort independently according to Mendel's law of independent assortment. This law states that the segregation of one pair of alleles for a gene is independent of the segregation of another pair of alleles for a different gene.

In a typical dihybrid cross involving two traits, such as flower color and seed shape, if both traits are controlled by different genes that assort independently, the expected phenotypic ratio of the offspring will be 9 (both dominant traits): 3 (dominant trait for the first and recessive for the second): 3 (recessive trait for the first and dominant for the second): 1 (both recessive traits).

This independent assortment leads to greater genetic diversity in the offspring, as different combinations of alleles can occur. Therefore, the observed phenotypic ratio confirms that the two traits being analyzed do not influence each other's distribution in the offspring.