What is the expected phenotype ratio in a dihybrid cross?

In a dihybrid cross, which involves two traits each governed by different genes, the expected phenotype ratio is 9:3:3:1. This ratio arises from the independent assortment of alleles during gamete formation, as stated by Mendel's second law of inheritance.

When you cross two organisms that are heterozygous for two traits (for example, AaBb x AaBb), you create a gamete pool combining all possible alleles from both traits. When these gametes combine during fertilization, the phenotypes of the offspring can manifest in multiple combinations:

• The first number in the ratio (9) represents the offspring showing both dominant traits.

• The second number (3) represents individuals showing the first dominant trait and the second recessive trait.

• The third number (3) represents individuals showing the second dominant trait and the first recessive trait.

• The final number (1) represents offspring displaying both recessive traits.

Thus, the ratio of phenotypes expected in the offspring of this dihybrid cross is 9:3:3:1, illustrating the variety of combinations that can arise when dealing with two independent traits.