Dihybrid Cross Punnett Square Calculator
Enter two parent genotypes — e.g. AaBb × AaBb — and get the full 16-box Punnett grid, the 9:3:3:1 phenotypic ratio, the 1:2:1:2:4:2:1:2:1 genotypic ratio, and exact per-phenotype probabilities. Monohybrid mode (4 boxes) included. Everything runs in your browser.
1. Enter the cross
Uppercase = dominant allele, lowercase = recessive allele. Each pair must be the same letter (e.g. Aa, Bb).
2. Name the traits (optional)
Results
Punnett grid
Phenotypic ratio
Genotypic ratio
How it works
Each parent produces 2n gamete types (n = number of genes): a dihybrid AaBb parent makes AB, Ab, aB, ab — each with probability 1/4. Crossing the two gamete lists gives a 4 × 4 = 16-box grid (2 × 2 = 4 for monohybrid). Every box is equally likely, so probabilities are exact box counts: e.g. 9 of 16 boxes = 9/16 = 56.25%. The calculator assumes independent assortment (genes on different chromosomes) and complete dominance.
Frequently asked questions
What is a dihybrid cross Punnett square?
A dihybrid cross Punnett square tracks two genes at once (for example AaBb x AaBb). Each parent makes 4 gamete types (AB, Ab, aB, ab), so the grid has 4 x 4 = 16 boxes, and each box is one equally likely offspring genotype.
What is the phenotypic ratio of a dihybrid cross (AaBb x AaBb)?
The classic dihybrid phenotypic ratio is 9:3:3:1. That means 9/16 (56.25%) of offspring show both dominant traits, 3/16 (18.75%) show dominant A with recessive b, 3/16 (18.75%) show recessive a with dominant B, and 1/16 (6.25%) show both recessive traits.
What is the genotypic ratio of AaBb x AaBb?
The dihybrid genotypic ratio is 1:2:1:2:4:2:1:2:1 across the 9 genotypes AABB, AABb, AAbb, AaBB, AaBb, Aabb, aaBB, aaBb and aabb. In a 16-box square that is counts of 1, 2, 1, 2, 4, 2, 1, 2 and 1, i.e. probabilities 1/16 (6.25%), 1/8 (12.5%) and 1/4 (25%). AaBb is the single most common genotype at 4/16 (25%).
What is the probability of the both-dominant phenotype (A_B_) in a dihybrid cross?
In a standard AaBb x AaBb dihybrid cross the both-dominant phenotype (for example round yellow seeds) has probability 9/16 = 56.25%.
What is the probability of a double-recessive (aabb) offspring?
In a standard AaBb x AaBb dihybrid cross the double-recessive genotype aabb appears in exactly 1 of the 16 boxes, so the probability is 1/16 = 6.25%.
How many boxes are in a dihybrid Punnett square?
A dihybrid Punnett square has 16 boxes: 4 gamete types from each parent (AB, Ab, aB, ab) crossed 4 x 4. A monohybrid cross (one gene, e.g. Aa x Aa) has 4 boxes: 2 gamete types crossed 2 x 2.
What are the ratios for a monohybrid cross (Aa x Aa)?
A monohybrid Aa x Aa cross fills a 4-box grid. The genotypic ratio is 1:2:1 (AA : Aa : aa), and the phenotypic ratio is 3:1, i.e. 3/4 (75%) show the dominant trait and 1/4 (25%) show the recessive trait.
What happens in a dihybrid testcross (AaBb x aabb)?
In a dihybrid testcross AaBb x aabb, the offspring genotypes AaBb, Aabb, aaBb and aabb each appear in 4 of the 16 boxes, giving a 1:1:1:1 genotypic and phenotypic ratio — each phenotype has probability 1/4 (25%).
What gametes does an AaBb parent produce, and with what probabilities?
An AaBb parent produces 4 gamete types — AB, Ab, aB and ab — each with probability 1/4 (25%), because each gene segregates its two alleles independently (law of segregation plus independent assortment).
When does the 9:3:3:1 ratio NOT apply?
The 9:3:3:1 ratio assumes the two genes assort independently (usually meaning they sit on different chromosomes) and that each trait shows simple complete dominance. Linked genes, incomplete dominance, codominance, or lethal allele combinations change the observed ratios.
Free tool by NRTechStudio