Punnett Square draws the square for the cross you type: the first parent’s gametes across the top, the second’s down the side, and every offspring genotype in the cells, with the genotype and phenotype ratios printed underneath. It handles one-gene crosses like Tt × Tt, dihybrid crosses like RrYy × RrYy in a 4 × 4 square, and X-linked crosses written on the X and Y chromosomes, with complete dominance, incomplete dominance or codominance. Alleles are set the way genetics texts set them, in italic letters with superscripts like Cᴿ and Iᴬ.
Teachers use it for genetics tests, worksheets and slides. Leave the cells, gametes, parents’ genotypes or ratios blank for students to fill in, shade the cells by phenotype in patterns that survive a photocopy, and put a question above the square.
Copy the figure straight into a test, worksheet or slide, or download it as a PNG or SVG. Printing the page prints
just the figure. Share link copies the page’s address with your settings in it, so anyone who opens it sees this
exact figure, and presets save settings you use often in your browser. It’s free, with no sign-up.
How do you fill in a Punnett square?
Split each parent’s genotype into the gametes it can make, one allele of each gene per gamete. Write the first parent’s gametes across the top and the second parent’s down the side, then fill each cell with the gamete above it plus the gamete beside it. For Tt × Tt the gametes are T and t on each side, and the cells are TT, Tt, Tt and tt.
What are the genotype and phenotype ratios of a Tt × Tt cross?
The genotype ratio is 1 TT : 2 Tt : 1 tt. With complete dominance TT and Tt look alike, so the phenotype ratio is 3 dominant : 1 recessive, such as 3 tall : 1 short. The generator prints both ratios under the square, as ratios, percentages or fractions.
Why does a dihybrid cross give a 9:3:3:1 ratio?
A parent heterozygous for two genes that assort independently, like RrYy, makes four kinds of gamete in equal numbers: RY, Ry, rY and ry. That gives a 4 × 4 square of 16 cells, of which 9 show both dominant traits, 3 show only the first, 3 show only the second, and 1 shows both recessive traits. Choose Dihybrid and type each parent with two genes.
How do I make an X-linked (sex-linked) Punnett square?
Choose X-linked and type the mother with two X chromosomes and the father with an X and a Y, each X carrying its allele as a superscript: X^B X^b × X^B Y. The Y carries no allele. Because sons get their only X from their mother, the phenotypes under the square are given separately for daughters and for sons.
What is the difference between incomplete dominance and codominance?
With incomplete dominance the heterozygote shows a blend of the two traits, as when red and white snapdragons give pink ones (CᴿCᵂ). With codominance both alleles show in full, as in type AB blood (IᴬIᴮ). Choose either under Dominance, then name each genotype’s phenotype. A small letter without a superscript, like i for type O, is recessive to the others.
How do I type superscripts like Cᴿ or Iᴬ?
Type ^ before a superscript and _ before a subscript, as in C^R C^W or R_1 R_2, or press Ctrl+. and Ctrl+, as in Google Docs. Pasted superscript letters work too. With incomplete dominance or codominance, a letter typed straight after the gene’s letter is read as a superscript (CR is Cᴿ) and a digit as a subscript (R1 is R₁).
Can I make a blank Punnett square for students?
Yes. Under Square, set Offspring to Blank, or to Some blank and click the cells students fill in, and tick the boxes to leave the gametes or the parents’ genotypes blank. Under Ratios, choose Blank line to give students a line for each ratio. Blank cells are never shaded, so the shading can’t give their answer away.
Biology Figures Punnett Square