What is the expected phenotypic ratio from a dihybrid cross?

In a dihybrid cross, two traits are considered, each controlled by two alleles. When both parents are heterozygous for two traits (for example, AaBb x AaBb), the resulting gametes can combine in various ways. This type of cross examines the inheritance patterns of two different characteristics simultaneously, leading to the formation of a 16-cell Punnett square.

Each cell in the Punnett square represents a possible genotype of the offspring. When all combinations are accounted for, the resulting phenotypes reveal a ratio of 9:3:3:1. This means that among the offspring, there are typically 9 instances showing both dominant traits, 3 instances showing the dominant trait of the first gene and the recessive trait of the second, 3 instances showing the recessive trait of the first gene and the dominant trait of the second, and 1 instance showing both recessive traits.

This 9:3:3:1 ratio emerges specifically when the two traits assort independently according to Mendel's law of independent assortment, a principle that underpins many aspects of genetics. Thus, this expected phenotypic ratio illustrates the complexity of inheritance and clearly demonstrates how multiple traits can combine in offspring.