Punnett Square Calculator

Type the genotype of parent 1, such as AaBb, and the genotype of parent 2, or switch on the test cross option. Use uppercase for dominant alleles and lowercase for recessive ones. The calculator lists the gametes, draws the square, and gives the genotype and phenotype ratios. For AaBb x AaBb it shows 16 boxes and the 9:3:3:1 phenotype ratio.

It shows the possible gametes from each parent, the grid of offspring genotypes, how many boxes there are of each genotype and phenotype, and the matching probabilities. For Aa x Aa the genotype ratio is 1:2:1 and the phenotype ratio is 3:1, so each offspring has a 75% chance of showing the dominant trait.

Write each parent's two alleles, put one parent's alleles across the top and the other's down the side, and fill each box with the matching pair. For Aa x Aa the boxes are AA, Aa, Aa and aa. That is 1:2:1 by genotype and 3:1 by phenotype. The calculator does this for any monohybrid pair and handles the case where a parent is homozygous.

Work out the four gametes of each parent, such as AB, Ab, aB and ab for AaBb, and place them along both sides of a 4 × 4 grid. Fill all 16 boxes. AaBb x AaBb gives 9:3:3:1 for the four phenotype classes, as OpenStax Biology shows for the round yellow pea cross. This page's 2x2 and 4x4 squares come from the same method.

Yes. Any cross with one gene uses a 2 × 2 square, four boxes in total. Enter a pair such as Aa x Aa or Aa x aa. If a parent is homozygous, its gamete is listed twice, so the square still has four boxes. For Aa x aa the four boxes give 1:1 by genotype, which is 50% Aa and 50% aa.

A 3 × 3 square does not come from a standard cross, because each parent makes 2, 4 or 8 equally likely gametes. Three genes need an 8 × 8 square with 64 boxes. This calculator accepts three genes, such as AaBbCc x AaBbCc, and reports the 64-box counts, though the grid is too wide to draw. Phenotype ratio: 27:9:9:3:9:3:3:1.

A test cross breeds an individual of unknown genotype with a homozygous recessive one. Because the partner can only pass on the recessive allele, the offspring show which alleles the unknown parent carried. If every offspring shows the dominant trait, the parent is probably AA. If about half show the recessive trait, it is Aa (1:1). Switch on the test cross option here.

Count the boxes for each genotype and reduce the counts by their greatest common divisor. For Aa x Aa the counts are 1 AA, 2 Aa and 1 aa, so the ratio is 1:2:1. For AaBb x AaBb the nine genotype counts are 1, 2, 1, 2, 4, 2, 1, 2, 1 out of 16. The calculator lists them in textbook order: homozygous dominant first, then heterozygous, then recessive.

Group boxes by how the trait looks. Under complete dominance AA and Aa look the same, so Aa x Aa has 3 boxes showing the dominant trait and 1 showing the recessive: 3:1. For two genes, group into four classes and count: AaBb x AaBb gives 9, 3, 3 and 1 out of 16.

Add the boxes where the recessive trait shows and divide by the total. For Aa x Aa it is 1 of 4, which is 25%. For AaBb x AaBb, a child that is recessive for both traits (aabb) has 1 of 16, or 6.25%. The calculator reports this as the all recessive chance.

A genotype is the pair of alleles an individual carries, such as Aa. A phenotype is the trait you can observe, such as round or wrinkled seeds. Under complete dominance, AA and Aa have different genotypes but the same phenotype, which is why the genotype ratio 1:2:1 collapses to the phenotype ratio 3:1. Both ratios are shown here.

It means one allele, written in uppercase, completely hides the other in a heterozygote. Aa looks the same as AA. This is the model behind Mendel's pea experiments, and it is the only model this calculator uses. Patterns such as incomplete dominance, codominance and sex linkage give different ratios and need different rules.

Not here. With incomplete dominance the heterozygote looks like a blend, so Aa x Aa gives three phenotypes in a 1:2:1 ratio instead of 3:1. You can still use the genotype ratio this calculator prints, because that part does not change: it is 1:2:1. Read each genotype as its own phenotype and the incomplete dominance pattern follows.

Not directly. Human ABO blood groups use three alleles, so a simple two-allele model does not apply. You can still draw a 2 × 2 square by hand with the alleles each parent carries. The genetics are a classroom exercise only. Blood group results from a real test, not a Punnett square, should be used for any medical or legal question.

Not reliably. Eye color depends on several genes plus other factors, so a single-gene square is a classroom simplification, not a prediction. A Punnett square is best for traits controlled by one or two genes with clear dominance. Use this calculator to learn and check homework, and do not use it to make medical, family or paternity decisions.

Yes. Any letters work, with uppercase as the dominant allele. For round and yellow peas use RrYy. Each gene needs two alleles of the same letter, so RrYy is valid and RrAa is also valid as two different genes. Parent 2 must use the same letters as parent 1. RrYy x rryy gives the 1:1:1:1.

One gene gives 4 boxes, two genes give 16 and three genes give 64, since each parent contributes 2 to the power of the number of genes gametes, counting repeats. OpenStax Biology gives the rules for heterozygous pairs: 2ⁿ gametes and 3ⁿ genotypes. The gene count table on this page shows the sizes.

They follow the textbook layout: homozygous dominant first, then heterozygous, then homozygous recessive, one gene at a time. For two genes the order is AABB, AABb, AAbb, AaBB, AaBb, Aabb, aaBB, aaBb, aabb. Phenotype classes run from dominant for every gene down to recessive for every gene. This keeps ratios like 9:3:3:1 in the familiar order.

No. A ratio describes the chance for each offspring, not a count you will see. A family of four children from Aa x Aa will often not show exactly one recessive child. Ratios like 3:1 appear when you have large numbers of offspring. Mendel's counts were close to, but not exactly, the ideal ratios.

It models complete dominance with up to three unlinked genes, each with two alleles. It does not handle incomplete dominance, codominance, multiple alleles, sex-linked genes, linked genes or mutation. It is a teaching tool. It makes no medical or paternity claims, and genetic questions about a person need a qualified professional.