Dihybrid Cross Calculator - Punnett Square

What this dihybrid cross calculator does

This calculator builds a 4×4 Punnett square for a dihybrid cross (two genes, A and B). It shows the offspring genotypes in each of the 16 cells and summarizes the genotype and phenotype probabilities.

Inputs and assumptions

• Each parent has a genotype for Gene A (AA, Aa, aa) and Gene B (BB, Bb, bb).
• This calculator assumes complete dominance for each gene: the uppercase allele (A or B) is dominant over the lowercase allele (a or b).

How gametes are formed

Each gamete contains one allele from Gene A and one allele from Gene B. For a single gene:

• If the parent is homozygous (AA), then \(P(A)=1\).
• If the parent is heterozygous (Aa), then \(P(A)=0.5\) and \(P(a)=0.5\).

For a dihybrid gamete, probabilities multiply: \[ P(\text{gamete }(A_iB_j)) = P(A_i)\cdot P(B_j) \] To build a standard 4×4 Punnett square, each parent’s gamete list is expanded to four entries (with duplicates) so the square always has 16 equally weighted cells.

Offspring genotypes from the Punnett square

Each cell combines one gamete from Parent 1 and one from Parent 2. For Gene A, the offspring genotype is the two alleles together (with uppercase first), for example: \[ A + a \rightarrow Aa \] The same is done for Gene B, then the full offspring genotype is concatenated (for example \(AaBb\)).

Genotype counts and probabilities

Each of the 16 cells represents one combination. If a genotype appears \(k\) times: \[ P(\text{genotype})=\frac{k}{16} \quad\text{and}\quad \%=\frac{k}{16}\cdot 100 \] The results table lists each unique genotype, its count out of 16, and its probability percentage.

Phenotypes under complete dominance

Under complete dominance:

• Gene A phenotype is dominant if the genotype contains \(A\) (AA or Aa), recessive only for \(aa\).
• Gene B phenotype is dominant if the genotype contains \(B\) (BB or Bb), recessive only for \(bb\).

The calculator reports the phenotype pattern as a simple label such as A dominant, B recessive.