Use this Dihybrid Cross Punnett Square Calculator to predict the possible genotypes and phenotypes of offspring for two traits. Select both parents’ genotypes at the A and B loci to generate their gametes, a 4 × 4 Punnett square, and the expected probabilities.
How the Dihybrid Cross Works
A dihybrid cross follows two genes at the same time. For example, a parent with the genotype AaBb can produce four possible gametes:
AB, Ab, aB, and ab
The calculator combines one gamete from each parent in every Punnett square cell. It then counts the resulting offspring genotypes and groups them into phenotypes.
An uppercase allele represents the dominant form of a trait. A recessive phenotype appears only when the offspring inherits two lowercase alleles at that locus.
Worked Example
Consider the cross:
AaBb × AaBb
Each parent can produce AB, Ab, aB, and ab gametes. Combining these gametes creates 16 equally likely cells.
Under complete dominance and independent assortment, the expected phenotype ratio is:
- 9/16 A_B_: dominant phenotype for both traits
- 3/16 A_bb: dominant A trait and recessive b trait
- 3/16 aaB_: recessive a trait and dominant B trait
- 1/16 aabb: recessive phenotype for both traits
This is the classic 9:3:3:1 dihybrid phenotype ratio.
Important Limitations
This calculator assumes that the two genes assort independently and that each trait follows complete dominance. Results may differ when genes are linked or when inheritance involves incomplete dominance, codominance, epistasis, or other gene interactions.
The probabilities are expected outcomes across many offspring. A small real-world group may not match the calculated ratio exactly because inheritance is random.