Punnett Square Calculator

How it is calculated

This is a monohybrid cross: one gene, two parents, each written as two letters (for example Aa), where a capital letter is the dominant allele and a lowercase letter the recessive one. Each parent passes on one of its two alleles with equal chance, so there are 2 × 2 = 4 equally likely combinations. The tool lists every combination, orders the letters in each genotype (capital first), counts identical genotypes and prints them as count genotype. The dominant percentage is the share of the four boxes containing at least one capital letter, dominant% = boxes with a capital / 4 × 100, and the recessive percentage is the rest. It assumes complete dominance and one gene on a normal chromosome; linked genes, incomplete dominance or sex-linked traits behave differently. Exactly two letters per parent are needed.

Common mistakes

• Typing a letter and its case inconsistently (A and a are the same gene; A and B are different genes).
• Entering more or fewer than two letters per parent, or mixing letters from two genes (a dihybrid cross needs a different method).
• Reading the 3:1 phenotype outcome as a guarantee for four children; the percentages are probabilities for each offspring.
• Confusing genotype ratio (1:2:1) with phenotype ratio (3:1).
• Using it for traits that show incomplete dominance or are sex-linked.