Final answer:
The 9:3:3:1 ratio in a dihybrid cross indicates that the alleles of two genes are segregating independently. This is consistent with Mendel's law of independent assortment where each trait is inherited separately, leading to the characteristic dihybrid ratio.
Step-by-step explanation:
When you see a 9:3:3:1 ratio in a dihybrid cross, it denotes that The alleles of two genes are segregating independently. This is observed in Mendelian genetics when two traits are involved, and the associated genes for these traits independently assort into gametes during meiosis. According to Mendel's law of independent assortment, each pair of alleles segregates independently of any other pair of alleles during gamete formation. This results in the dihybrid phenotypic ratio that totals 16, with no intergenic interactions affecting the outcome.
Isolating each trait in our dihybrid cross example, if one trait follows a phenotypic ratio of 3:1, then considering both traits together results in a ratio of (3/4) × (3/4) for the dominant phenotype of both traits, equaling 9/16. The 9:3:3:1 ratio occurs because the alleles for each gene assort independently into the gametes, ultimately producing the characteristic phenotypic ratios when fertilization occurs.