Punnett Square Calculator

It builds a monohybrid Punnett square, a cross for one gene with two alleles. Each parent passes one of its two alleles into every gamete, and the 2x2 grid pairs each allele from parent 1 with each allele from parent 2 to list all four possible offspring.

Use exactly two letters of the same trait, such as Aa, BB or aa. A capital letter marks the dominant allele and lower case the recessive allele. Both parents must use the same letter, so Aa crossed with Bb is rejected because they describe different genes.

No. The tool normalises every offspring cell so the dominant allele comes first, turning aA into Aa. That is why an entry like aA and a tidy Aa produce the same grid and the same ratios.

The classic heterozygous cross gives a 1:2:1 genotype ratio of AA to Aa to aa, which the tool reports as 1 AA : 2 Aa : 1 aa. Because one dominant allele is enough to show the dominant trait, the phenotype ratio is 3 dominant to 1 recessive.

It scans each of the four grid cells for a capital letter. Any cell with at least one capital counts as showing the dominant phenotype, and cells with two lower case letters count as recessive. The tally is reported out of four, for example 3 dominant to 1 recessive.

No. This tool is strictly monohybrid, one gene at a time, so it always draws a 2x2 grid. A dihybrid cross tracks two genes together and needs a 4x4 grid of sixteen cells, which is a different calculation.

Not directly. It classifies a phenotype as dominant whenever a capital allele is present, which is the simple complete-dominance model. For incomplete dominance or codominance the heterozygote shows its own blended or joint phenotype, so read the genotype ratio and interpret the middle class yourself.

Anything that is not two letters of one trait. A single letter, three letters, a digit or a symbol is rejected, and two different trait letters like Aa and Bb are refused. Spaces are ignored, so A a is read as Aa.

No. The cross is computed locally with plain string logic, so the genotypes you enter stay on your device and nothing is sent to a server.