What is the ratio of a dihybrid cross?

Dihybrid cross is a cross between two different genes with distinct features. The hybrid cross is made of both heterozygous organisms.

• The concept of a dihybrid cross was developed by Gregor Mendel after he observed spherical or wrinkled pea plants with green or yellow seeds. 
• In a dihybrid cross, each attribute is represented by a separate pair of alleles.
• The children that are produced by these crosses in the F1 generation are all heterozygous.
• A parent has a homozygous dominant allele and the other has a homozygous recessive allele.

The crossing of two heterozygous individuals leads to a predictable ratio in the offspring for both genotype and phenotype. The expected ratio of dihybrid crossing is 9:3:3:1. Deviations from these ratios indicate that either the two traits are linked or one or both of them have a non-Mendelian mode of inheritance.

Ratio of dihybrid cross

In the standard Mendel experiment, the phenotypic ratio of the dihybrid cross is 9:3:3:1. 

• In this case, the 2 allelic pairings are distributed separately into gametes.
• The genotypic ratio of a dihybrid cross is 1:2:2:4:1:2:1:2:1.

The expected phenotypic ratio of the dihybrid cross of 9:3:3:1 is broken down into – 

• 9 is the proportion of individuals with both dominant traits.
• Then, the 3 is the number of individuals with the first dominant trait and the second recessive trait.
• The second 3 are the individuals with the first recessive trait and second dominant trait.
• The 1 represents the homozygous individuals with both recessive traits.

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